Methods for the purification of l-glufosinate

ABSTRACT

Compositions and methods for isolating L-glufosinate from a composition comprising L-glufosinate and glutamate are provided. The method comprises converting the glutamate to pyroglutamate followed by the isolation of L-glufosinate from the pyroglutamate and other components of the composition to obtain substantially purified L-glufosinate. The composition comprising L-glufosinate and glutamate is subjected to an elevated temperature for a sufficient time to allow for the conversion of glutamate to pyroglutamate, followed by the isolation of L-glufosinate from the pyroglutamate and other components of the composition to obtain substantially purified L-glufosinate. The glutamate alternatively may be converted to pyroglutamate by enzymatic conversion. The purified L-glufosinate is present in a final composition at a concentration of 90% or greater of the sum of L-glufosinate, glutamate, and pyroglutamate. In some embodiments, a portion of the glutamate in the starting composition may be separated from the L-glufosinate using a crystallization step. Solid forms of L-glufosinate materials, including crystalline L-glufosinate ammonium, are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 16/631,963, which is a U.S. National Phase of PCT/US2018/042503,filed on Jul. 17, 2018, which claims priority to U.S. Provisional Pat.Appl. No. 62/533,944, filed on Jul. 18, 2017, and U.S. Provisional Pat.Appl. No. 62/653,736, filed on Apr. 6, 2018; all of the aforementionedapplication are hereby incorporated herein by reference in theirentireties.

FIELD

Described herein are methods for the purification of L-glufosinate.

BACKGROUND

The herbicide glufosinate is a non-selective, foliarly-applied herbicideconsidered to be one of the safest herbicides from a toxicological orenvironmental standpoint. Current commercial chemical synthesis methodsfor glufosinate yield a racemic mixture of L- and D-glufosinate (Duke etal. 2010 Toxins 2:1943-1962). However, L-glufosinate (also known asphosphinothricin or (S)-2-amino-4-(hydroxy(methyl)phosphonoyl)butanoicacid) is much more potent than D-glufosinate (Ruhland et al. (2002)Environ. Biosafety Res. 1:29-37).

Therefore, methods are needed to produce only or primarily the active,L-glufosinate form. Previously, effective methods to generate pureL-glufosinate, or a mixture of D- and L-glufosinate enriched forL-glufosinate, have not been available.

SUMMARY

Compositions and methods for isolating L-glufosinate from a compositioncomprising L-glufosinate and glutamate are provided. The methodcomprises converting the glutamate to pyroglutamate followed by theisolation of L-glufosinate from the pyroglutamate and other componentsof the composition to obtain substantially purified L-glufosinate. Inone embodiment, the composition comprising L-glufosinate and glutamateis subjected to an elevated temperature for a sufficient time to allowfor the conversion of glutamate to pyroglutamate, followed by theisolation of L-glufosinate from the pyroglutamate and other componentsof the composition to obtain substantially purified L-glufosinate. Inanother embodiment, the glutamate is converted to pyroglutamate byenzymatic conversion followed by removal of the pyroglutamate from thecomposition by ion exchange to obtain a composition comprisingsubstantially purified L-glufosinate. The volume of the composition maybe reduced to obtain a concentrated solution of L-glufosinate or reducedto obtain a solid powder of L-glufosinate. In one embodiment, thepurified L-glufosinate is present in the final composition at aconcentration of 70% or greater, 80% or greater, or 90% or greater ofthe sum of L-glufosinate, glutamate, and pyroglutamate. In someembodiments, a portion of the glutamate in the starting composition isseparated from the L-glufosinate by a crystallization step prior toconverting the glutamate to pyroglutamate. Also provided herein aremethods for the isolation of 2-oxoglutaric acid (also referred to hereinas 2-oxoglutarate) from the composition after L-glufosinate has beenremoved. 2-Oxoglutaric acid can be removed, for example, by ion exchangeto obtain a composition of substantially pure 2-oxoglutaric acid whichthen can be converted easily to substantially pure succinic acid.

The methods described herein produce a substantially pure composition ofL-glufosinate. In further embodiments, the methods produce asubstantially pure composition of 2-oxoglutaric acid. Crystalline formsof L-glufosinate materials are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an XRPD pattern collected with Cu-Kα radiation forL-glufosinate ammonium Form A.

FIG. 2 shows thermal data collected for L-glufosinate ammonium Form A bythermogravimetric analysis (top trace) and differential scanningcalorimetry (bottom trace).

FIG. 3 shows an XRPD pattern collected with Cu-Kα radiation forL-glufosinate Form B.

FIG. 4 shows thermal data collected for L-glufosinate Form B bythermogravimetric analysis (top trace) and differential scanningcalorimetry (bottom trace).

FIG. 5 shows an XRPD pattern collected with Cu-Kα radiation forL-glufosinate ammonium Form C.

FIG. 6 shows thermal data collected for L-glufosinate ammonium Form C bythermogravimetric analysis (top trace) and differential scanningcalorimetry (bottom trace)

FIG. 7 shows an XRPD pattern collected with Cu-Kα radiation forL-glufosinate Form D.

FIG. 8 shows thermal data collected for L-glufosinate Form D bythermogravimetric analysis (top trace) and differential scanningcalorimetry (bottom trace).

FIG. 9 shows an XRPD pattern collected with Cu-Kα radiation forL-glufosinate hydrochloride Form E.

DETAILED DESCRIPTION

Compositions and methods for the production of a substantially purifiedcomposition of L-glufosinate (also known as phosphinothricin or(S)-2-amino (hydroxy(methyl)phosphonoyl)butanoic acid) are provided.U.S. patent application Ser. No. 15/445,254 (“the '254 application”)filed Feb. 28, 2017, herein incorporated by reference, is drawn tocompositions and methods for the production of L-glufosinate. The methodinvolves the oxidative deamination of D-glufosinate to PPO(2-oxo-4-(hydroxy(methyl)phosphinoyl)butyric acid), followed by thespecific amination of PPO to L-glufosinate, using an amine group fromone or more amine donors. By combining these two reactions, theproportion of L-glufosinate can be substantially increased in a racemicglufosinate mixture. Thus, the method of the '254 application can usethe racemic D-/L-glufosinate mixture as the starting mixture and convertthe inactive D-form into the active L-form. The method of the '254method results in a composition comprising a mixture of L-glufosinate,PPO, and D-glufosinate, where L-glufosinate is the predominant compoundamong the mixture of L-glufosinate, PPO, and D-glufosinate. Glutamate(which refers to L-glutamate, D-glutamate, or a combination of the two),also known as glutamic acid (which refers to L-glutamic acid, D-glutamicacid, or a combination of the two) may be present in the compositionwhen glutamate or L-glutamate is used as the amine donor in theamination of PPO to L-glufosinate.

The separation of L-glufosinate from 2-oxoglutarate, PPO, and glutamicacid in the post-reaction mixture typically requires multiple operationsbecause the chemical structures and chemical properties of thesecomponents are very similar. L-glutamic acid presents the main challengebecause it is present in a high concentration relative to L-glufosinateand is structurally similar to L-glufosinate.

I. Methods of Purification

Provided herein are methods for purifying L-glufosinate from acomposition that includes L-glufosinate and glutamate. The methodsinclude converting glutamate to pyroglutamate to facilitate isolation ofL-glufosinate. The glutamate can be converted to pyroglutamate bysubjecting the composition to an elevated temperature for a sufficientperiod of time to convert the majority of glutamate to pyroglutamate(which is also referred to herein as pyroglutamic acid). See, forexample, PCT 2010/013242, U.S. 2003/0018202, Corma et al. (2007) Chem.Rev. 107:2411-2502, Purwaha et al. (2014) Anal. Chem. 86(12):5633-5637,Dubourg et al. (1956) Bulletin de la Societe Chimique de France1351-1355, and Helv. Chim. Acta (1958) 181, all of which are hereinincorporated by reference. Alternatively, the glutamate can be convertedto pyroglutamate by enzymatic transformation. Upon exposing theresulting mixture to cation exchange resin, glufosinate (and, whenpresent, glutamate) typically adsorbs more strongly than pyroglutamicacid. Upon exposing the resulting mixture to anion exchange resin,pyroglutamic acid typically adsorbs more strongly than glufosinate.

For non-enzymatic conversion of glutamic acid to pyroglutamic acid,acidic pH is preferred. If the reaction mixture is not already acidic,an acid can be used to adjust the pH of the reaction mixture. Suitableacids that can be used to adjust the pH include hydrochloric acid,sulfuric acid, trifluoroacetic acid, phosphoric acid, acetic acid, orany other material with a pKa<5. See, for example, DE 3920570 C2, whichis herein incorporated by reference. The pH can be adjusted to a valuefrom about 0.4 to about 7, a value from about 1.0 to about 6.0, a valuefrom about 2.0 to about 5.0, or a value from about 2.5 to about 3.5.

As indicated, the glutamate can be converted to pyroglutamate bysubjecting the composition to an elevated temperature for a sufficientperiod of time to convert the majority of glutamate to pyroglutamate.The elevated temperature can be at least 100° C., at least 110° C., atleast 120° C., at least 130° C., at least 140° C., at least 150° C., atleast 160° C., at least 170° C., at least 180° C., or at least 190° C.Typically, the elevated temperature can range from about 120° C. toabout 180° C. Any method suitable for increasing the temperature of amaterial to an elevated temperature, as described above, can be used andis encompassed within the methods described herein. For example, theelevated temperature can be reached by heating the mixture orcomposition in an autoclave under modest pressure; heating neat or in ahigh boiling inert solvent using a heating mantle, boiling plate, oil orsilicone bath; recirculating fluid in a jacketed reactor; or any othermethods used to apply heat as known to those skilled in the art. The useof heat guns and open flames are also encompassed within these methods.

As used herein, the term “majority” of a component refers to an amountof at least 50% by weight of the component. For example, the term“majority” can refer to 50 wt. % or more, 55 wt. % or more, 60 wt. % ormore, 65 wt. % or more, 70 wt. % or more, 75 wt. % or more, 80 wt. % ormore, 85 wt. % or more, 90 wt. % or more, 95 wt. % or more, or 99 wt. %or more of the component.

As used herein, the term “substantially pure” or “substantiallypurified,” as related to a particular component, means that thecomponent is present in a composition in an amount of 70% or greater,75% or greater, 80% or greater, 85% or greater, 90% or greater, or 95%or greater of the sum of the total components present in thecomposition.

The conversion of glutamate to pyroglutamate is allowed to proceed for asufficient period of time such that a majority of the glutamate isconverted to pyroglutamate. Generally, the majority of glutamate isconverted in about 2 hours to about 20 hours (e.g., about 2 hours toabout 15 hours). That is, the conversion time under elevatedtemperatures can be about 2 hours or greater, about 3 hours or greater,about 4 hours or greater, about 5 hours or greater, about 6 hours orgreater, about 7 hours or greater, about 8 hours or greater, about 9hours or greater, about 10 hours or greater, about 11 hours or greater,about 12 hours or greater, about 13 hours or greater, about 14 hours orgreater, about 15 hours or greater, about 16 hours or greater, about 17hours or greater, about 18 hours or greater, about 19 hours or greater,or about 20 hours.

The reaction mixture can be concentrated before or after convertingglutamic acid to pyroglutamic acid. Any means of concentration known bythose skilled in the art can be used, such as distillation, includingdistillation under vacuum, thin film evaporation, wiped filmevaporation, pervaporation, reverse osmosis, and the like. Water andother volatile materials removed by concentration can be recycled foruse in the process, if desired. Optionally, the reaction mixture can beconcentrated during the conversion of glutamic acid to pyroglutamic acidby removing water vapor and other volatile material from the reactionmixture, as this mode of operation utilizes time and energy mostefficiently.

Following the conversion of glutamic acid to pyroglutamic acid, thereaction mixture can be treated with an adsorbent or other solidmaterial to reduce or remove color without any loss of L-glufosinate.Suitable adsorbents include activated charcoal (also known as activatedcarbon), bone char, and the like. Polymeric materials, such as thosedescribed by U.S. Pat. No. 4,950,332, which is herein incorporated byreference, or other ion exchange resins can be particularly useful incommercial operation for the decolorization of the reaction mixture.Other treatments known to those skilled in the art can be used todecolorize the reaction mixture.

In one example, various amounts of activated carbon may be added toportions of the same reaction mixture after the conversion topyroglutamic acid. After mixing for approximately 20 minutes at roomtemperature, the activated carbon can be filtered on top of a bed ofpre-washed Celite®. The filter cake is then washed with water and thecake wash combined with the filtrate. In this example when the filtratewas then checked for L-glufosinate recovery relative to an untreatedsample using pyroglutamic acid as an internal standard, the table belowshows the recovery and color observations.

Wt % activated carbon L-glufosinate recovery Color observation 0.25 104%Slightly orange 0.5 103% Slightly orange 1.0  98% Slightly orange 3.0103% No color 5.0  98% No color

In one embodiment, after the conversion of glutamic acid to pyroglutamicacid, the reaction mixture can be cooled to a temperature below 20° C.In a preferred embodiment, the reaction mixture is adjusted to about pH3 using sulfuric acid prior to the reaction, then adjusted to about pH 6with sodium hydroxide after the conversion of glutamic acid topyroglutamic acid, and then cooled to a temperature just above thefreezing point of the reaction mixture (e.g., about 5° C. or below).Optionally, the reaction mass is concentrated and/or decolorized asdescribed above prior to cooling. The advantage to this procedure isthat sodium sulfate will precipitate or crystallize from the reactionmixture. The solid sodium sulfate, which could be in anhydrous orhydrated form, is substantially pure and can be removed from thereaction mixture by filtration, centrifugation, or any other suitablemeans to separate solids from liquids known by those skilled in the art.Optionally, seed crystals of anhydrous or hydrated sodium sulfate can beadded to the mixture to initiate crystallization.

Salt removal achieved by the combination of evaporative concentration,cooling crystallization and filtration is not particularly efficientwhen compared to membrane separation processes. Membrane separators areemployed in many industries to achieve a variety of separations as thetechnology is well developed; a description of common techniques can befound in “Unit Operations of Chemical Engineering”, W. L. McCabe, J. C.Smith and P. Harriott, sixth edition; McGraw-Hill, 2001; ISBN:0070393664. Reverse osmosis and ultrafiltration, described in“Ultrafiltration Handbook”, M. Cheryan, Technomic Publishing, 1986;ISBN: 0877624569, are examples of membrane separations that arepracticed at the commercial scale. The term “nanofiltration” is used todescribe separations that use membranes with pores that are larger thanthose in reverse osmosis membranes but smaller than those inultrafiltration membranes. Membrane pore size is an important parameterbecause in many applications the membrane is selected to separatecomponents of a mixture based on the difference in size their sizes.U.S. Pat. No. 5,447,635, incorporated herein by reference, discloses amembrane separation process in which salts and other low molecularweight solutes are removed from an aqueous solution of Iopamidol, anX-ray contrast agent; at the same time, the solution of Iopamidol isconcentrated. Membrane separation processes can be used in combinationwith other unit operations to optimize the purity of the product stream.U.S. Pat. No. 5,811,581, incorporated herein by reference, discloses aprocess in which the aqueous stream containing Iopamidol is firstpurified by a chromatographic separation followed by a membraneseparation process; examples teach that Iopamidol can be obtained inhigh purity and high yield using the combined techniques.

Membranes may be used to remove inorganic salts and some water from theL-glufosinate mixture either before or after the conversion of glutamicacid to pyroglutamic acid. The mixture containing L-glufosinate may bepumped through the membrane separator whereupon the inorganic salts andsome water travel through the membrane away from the L-glufosinatemixture. Salts may include the sodium salt of the acid used to adjustthe pH before the glutamic acid conversion, for example, sodium sulfate,if sulfuric acid is used to adjust pH, or sodium chloride, ifhydrochloric acid is used to adjust pH. Selected membranes may allowsome glutamic acid and/or pyroglutamic acid to pass through along withsalt and water.

Suitable membranes may be made from natural or synthetic polymers,including but not limited to cellulose, polycarbonate, polyethylene,polypropylene, polysulfone, polylactic acid, polyacrylamide,polyvinylidine and the like. The polymers may be chemically modified ifdesired. Alternatively, a ceramic membrane may be used. U.S. Pat. Nos.3,556,305; 3,556,992; 3,628,669; and 3,950,255 disclose methods ofmaking membranes and their use in separations processes. Standardequipment for membrane separations can be used for the membraneseparation. Those skilled in the art will recognize that membranes canbe used in a number of configurations, including but not limited to,flat sheets for plate-and-frame configuration or hollow fiber tubes forshell-and-tube configuration. Spiral wound membrane modules can beparticularly efficient when used for this purpose. U.S. Pat. Nos.3,228,876; 3,401,798; and 3,682,317 disclose several membraneconfigurations suitable for commercial operation.

The L-glufosinate mixture may be pumped through the membrane separatorin a single pass or several passes to reach the desired level ofdesalting and concentration. The resulting desalted and concentratedL-glufosinate mixture can be further purified if desired.

The L-glufosinate can be isolated from the pyroglutamate and any othercomponents of the composition to obtain a composition of substantiallypurified L-glufosinate. The terms “substantially purified L-glufosinate”or “substantially pure L-glufosinate” are used to indicate that theamount of L-glufosinate in the final composition is 70% or greater, 75%or greater, 80% or greater, 85% or greater, 90% or greater, or 95% orgreater of the sum of L-glufosinate, glutamate, pyroglutamate, and anyother component in the final composition.

In some cases, glutamate can be converted to pyroglutamate by enzymatictransformation. See, for example, U.S. Pat. No. 3,086,916, hereinincorporated by reference. In this manner, a glutaminyl-peptidecyclotransferase, (for example, E.C. 2.3.2.5), can be added to thecomposition comprising L-glufosinate and glutamate for a sufficient timeto allow for the conversion of glutamate to pyroglutamate. The amount oftime sufficient for conversion will vary depending on the activity andthe concentration of enzyme used in the reaction. Generally, the timewill be at least 2 hours, at least 4 hours, at least 6 hours, at least 8hours, at least 10 hours, at least 12 hours, or more.

In some embodiments, a crystallization step can be used to remove aportion of the glutamate prior to conversion of the remaining glutamateto pyroglutamate. In this manner, in a first step, a portion of theglutamate can be crystallized and removed from the starting compositionby filtration, centrifugation, or any other suitable solid-liquidseparation process known by those skilled in the art. For example, 0.1wt. % or greater, 0.5 wt. % or greater, 1 wt. % or greater, 5 wt. % orgreater, 10 wt. % or greater, 15 wt. % or greater, or 20 wt. % orgreater of the glutamate present can be crystallized and removed fromthe starting composition. The crystallized glutamate can be reused, forexample, in a subsequent enzymatic transformation of D-glufosinate.

For crystallization, the composition can be adjusted to a pH of fromabout 3 to about 5 (e.g., from about 3.5 to about 4.5, from about 3.5 toabout 3.8, or from about 3.7 to about 4.2) with the addition of an acid.Suitable acids for adjusting the pH include hydrochloric acid, sulfuricacid, trifluoroacetic acid, phosphoric acid, acetic acid, or any othermaterial with a pKa<5. See, for example, DE 3920570 C2, which is hereinincorporated by reference.

In some examples, the temperature of the composition is carefullycontrolled. In this manner, the composition can be heated to atemperature of about 30° C., about 35° C., about 40° C., and the likefollowed by the addition of acid. The acid, for example, concentratedhydrochloric acid or sulfuric acid, is added either continuously or inportions at a slow rate to a suitable container which holds the reactionmixture. Agitation of the mixture during the acid addition is preferredand may be accomplished by any suitable means. With sufficient mixing,the addition of acid to the mixture is generally insensitive to the rateof addition when the pH of the mixture exceeds about pH 5 becauseprecipitation or crystallization is generally not observed at above pH5. In the laboratory, using suitable equipment, the acid addition belowpH 5 is performed at a dropwise rate, dropwise rate meaning less than0.1 mL, less than 0.2 mL, less than 0.3 mL, less than 0.4 mL portionsevery several seconds, such that the crystallization of glutamic acidbegins before the end of the concentrated hydrochloric acid or sulfuricacid addition. For example, when practiced in the laboratory,approximately 35 mL to 40 mL of 10 M sulfuric acid can be added dropwiseover a period of time (e.g., 15 to 20 minutes) to a batch approximately1 L in volume.

The reaction mixture can then be heated to an elevated temperature ofabout 35° C. to about 90° C. (e.g., about 40° C. to about 80° C., about50° C. to about 70° C., or about 55° C. to about 65° C.), and held atthe elevated temperature for at least about 20 minutes (e.g., at leastabout 25 minutes or at least about 30 minutes). In some examples, someof the heat associated with the addition of the acid is not immediatelyremoved and the reaction mixture is allowed to slowly self-heat. Afterholding at the elevated temperature as described, the resultingcomposition is then slowly cooled over time to 0° C. Optionally, thecomposition can be cooled to 0° C. over a duration of several minutes toseveral days, and can be held for at least about 30 minutes, about 45minutes, about 50 minutes, about 60 minutes, over multiple hours, orover multiple days before filtering the reaction mass.

One advantage of controlling the temperature as described above is toproduce high purity glutamate crystals which are easy to filter.Optionally, the crystallization method could be performed with thepresence of glutamic acid seed crystals (e.g., glutamic acid crystalsadded to the mixture during the acid addition, glutamic acid crystalsleft over from a previous batch, or glutamic acid crystals present in acontinuous crystallizer) to assist with the growth of crystals to a sizesuitable for easy filtration.

Another advantage of controlling the temperature as described above,more particularly of reducing the temperature below room temperature, isthat more glutamic acid will crystallize and therefore the quantity ofglutamic acid which remains in the filtrate will be reduced. Optionally,a water miscible solvent could be added to further reduce the solubilityof glutamic acid in the mixture. The addition of a water misciblesolvent also allows lower temperatures to be reached without freezing ofthe mixture.

The present method of crystallizing glutamic acid from the reaction massor starting composition greatly reduces the amount of glutamic acid insolution. The residual glutamic acid in the reaction mixture orcomposition can be converted to pyroglutamic acid at an elevatedtemperature as described above. The resulting pyroglutamic acid iseasily separated from L-glufosinate in a single ion exchange step (i.e.,either a cation or an anion exchange, both cation exchange and anionexchange steps are not required), or other separation approaches, andthis results in a high purity L-glufosinate with low levels of glutamicacid.

In one embodiment, an anion exchange resin is used to purifyL-glufosinate from pyroglutamic acid, 2-oxoglutarate, and PPO at aslightly basic, neutral, or acidic pH at ambient or elevatedtemperatures. In some examples, the interaction between L-glufosinateand the anion exchange resin may not be as strong as the interactionsbetween the anion exchange resin and each of the 2-oxoglutarate, PPO,and pyroglutamate. The difference in interaction behavior can be used toeffect purification of the L-glufosinate. In this procedure, the anionexchange resin can be charged to a suitable container, such as a tank ora column. In some examples, the anion exchange resin is converted to ahydroxy form using an aqueous solution of a suitable inorganic base,such as sodium hydroxide or potassium hydroxide. In some instances, theanion resin is converted to sulfate of bisulfate form using sulfuricacid or inorganic sulfate or bisulfate salts. The resin is thenequilibrated at the desired temperature through either external heating(e.g., flowing a heat transfer fluid in the jacket of the container) orby pumping fluid at the desired temperature through the container orboth. The resin is equilibrated at the desired pH using dilute acid,dilute base, and/or water. The reaction mixture can be obtained from theglutamic acid cyclization step, which optionally could be concentratedas described above, and/or which optionally could be decolorizedfollowing a procedure described above, can be adjusted to the same pH asthe resin. The reaction mixture can also be adjusted to the sametemperature as the resin and pumped through the anion exchange resin inthe container, typically in a down flow fashion. Effluent exiting thecontainer can be collected in portions. Portions of the effluentcontaining a majority of L-glufosinate can be combined together to forma solution of substantially purified L-glufosinate. Without being boundto any particular theory, pyroglutamic acid, 2-oxoglutaric acid, PPO,and other impurities interact with the anion exchange resin such thatthe components travel through the column at different rates compared toL-glufosinate thereby allowing substantially purified L-glufosinate tobe collected in a separate solution.

Many kinds of commercially available anion exchange resins can be usedto prepare substantially purified L-glufosinate, as described above.Examples of suitable resins include those constructed of a cross-linkedcopolymer backbone (e.g., made with a monovinyl monomer such as styrene,acrylate, and the like, and a polyvinyl crosslinking agent such asdivinylbenzene, etc.). U.S. Pat. Nos. 3,458,976 and 6,924,317, both ofwhich are incorporated herein by reference, disclose other monovinylmonomers and polyvinyl crosslinking agents that could be used togenerate suitable copolymer backbone material. Resins made in a varietyof porosities, including microporous and macroporous, can be used. Theterms “microporous” and “macroporous” refer to the size range of poresin a solid particle. Two common methods for determining pore size arenitrogen adsorption-desorption and mercury porosimetry (see W. C. Connoret al. 1986 Langmuir 2(2):151-154). It is understood by those skilled inthe art that macroporous materials contain both macropores andmesopores; mesopores range in size from about 20 angstroms to about 500angstroms and macropores are greater than about 500 angstroms in size.Microporous materials have micropores which are less than 20 angstromsin size. See PCT/US2016/063219, which is incorporated herein byreference. Gel type resins, such as those described by U.S. Pat. Nos.4,256,840 and 5,244,926, both of which are incorporated herein byreference, are considered to be microporous and can be used as well.Resin particles in the form of a bead, meaning spherical or nearlyspherical in shape, are particularly useful in the present method. Beadsmay be uniform (also known as “monodisperse”), Gaussian, or polydispersein particle size distribution. “Uniform” or “monodisperse” means atleast 90 volume percent of the beads have a particle diameter from about0.8 to about 1.2, and more preferably 0.85 to 1.15 times the volumeaverage particle diameter. See PCT/US2016/063220, incorporated herein byreference.

Resins can be converted to anion exchange resins by functionalizationwith one or more types of amines. One method by which resins can befunctionalized is by subjecting the copolymer to a chloromethylationreaction followed by reaction with primary amines, secondary amines,tertiary amines, aminoalcohols, polyamines, or ammonia, as described inU.S. Pat. No. 6,924,317. Anion exchange resins with an anion capacity offrom about 0.1 to about 4 milliequivalents per gram wherein anioncapacity is measured according to ASTM D2187-94 (reapproved 2004), aresuitable for use in the present method. Resins functionalized withprimary and secondary amines are known to those skilled in the art asweak base anion resins. Resins functionalized with tertiary amines andtertiary polyamines, known as strong base anion exchange resins to thoseskilled in the art, are particularly suitable for use in the presentmethod. In one embodiment, a mixture of strong base anion exchangeresins and weak base anion exchange resins is used to producesubstantially purified L-glufosinate.

The size of the resin particles can be selected to achieve purificationat an acceptable pressure drop in the equipment used for the ionexchange process. The preferred median volume average diameter of resinparticles used in the method ranges from about 10 microns to about 2000microns; a particularly useful range of median diameter is from about100 microns to about 1000 microns. Examples of suitable resins include,but are not limited to, DOWEX™ MARATHON™ A, DOWEX™ MONOSPHERE™ 550A,DOWEX™ MONOSPHERE™ MSA, DOWEX™ XUR-1525-L09-046, an experimental,gel-type, uniform particle size in the range of 300 microns, strong baseanion resin, Type I (trimethylamine quaternary ammonium, in the chlorideform, obtained from the Dow Chemical Company), as well as others knownto those skilled in the art.

In some examples, an elevated temperature is used for the separation.The reaction mixture fed to the column, as well as the column itself,can be maintained at a temperature from about 25° C. to about 30° C.,from about 30° C. to about 35° C., from about 35° C. to about 40° C.,from about 45° C. to about 50° C., from about 50° C. to about 55° C.,from about 55° C. to about 60° C., from about 60° C. to about 65° C., orfrom about 65° C. to about 70° C. The temperature of the column can bemaintained by flowing a heating fluid in a jacketed column, using aheating mantle applied to the column walls, maintaining the columninside a heated enclosure or by any other means of heating known tothose skilled in the art.

The separation can be conducted in a pH range from about pH 0.4 to pH 8;that is, at about pH 0.4, at about pH 0.6, at about pH 1, at about pH 2,at about pH 3, at about pH 4, at about pH 5, at about pH 6, at about pH7, or about pH 8. Acids that can be used for the pH adjustment includehydrochloric acid, sulfuric acid, phosphoric acid, trifluoroacetic acid,acetic acid, methanesulfonic acid, and the like. Bases that can be usedfor the pH adjustment include sodium hydroxide, potassium hydroxide,ammonium hydroxide, and the like.

As known in the field of ion exchange separations, resins can beregenerated for reuse. U.S. Pat. No. 3,458,439, for example, describesmethods for the regeneration of anion resins. In such a regenerationprocess, the resin is treated with a solution or solutions which causepreviously adsorbed components to desorb from the resin and return theresin to the preferred form for the separation. Typically, the solutionscontain either an acid or a base and optionally an inorganic salt suchas sodium chloride, sodium phosphate, sodium sulfate, ammonium sulfate,and the like. In one embodiment, an anion exchange resin can beregenerated with caustic brine (i.e., a mixture of sodium hydroxide andsodium chloride), acidic brine (i.e., a mixture of hydrochloric acid andsodium hydroxide), sulfuric acid with or without sodium chloride, orsodium chloride alone. Useful compositions of caustic brine includeconcentrations of sodium hydroxide from about 0.01 M to about 0.5 M andconcentrations of sodium chloride from about 0.1 M to about 1.5 M.Useful compositions of acidic brine include concentrations ofhydrochloric acid from about 0.01 M to about 0.5 M and concentrations ofsodium chloride from about 0.1 M to about 1.5 M. In some examples,acidic brine includes sulfuric acid concentrations from about 0.1 M toabout 1.5 M and sodium chloride concentrations from about 0.1 M to about1.5 M. Optionally, water adjusted to pH 1 with sulfuric acid can beused.

Certain methods of regeneration can be advantageous when used in thepractice of the methods described herein. The methods used to producesubstantially purified L-glufosinate, when combined with anion exchangeresin regeneration method, can also be used to produce substantiallypurified 2-oxoglutaric acid (also referred to herein as 2-oxoglutarate).By substantially purified 2-oxoglutarate or substantially pure2-oxoglutarate it is intended that the amount of 2-oxoglutarate in thefinal composition is 70% or greater, 75% or greater, 80% or greater, 85%or greater, 90% or greater, or 95% or greater than the sum of2-oxoglutaric acid, L-glufosinate, glutamate, succinic acid, andpyroglutamate in the final composition. The substantially purified2-oxoglutaric acid can be easily and efficiently converted to succinicacid (which is used as a food additive and a dietary supplement) afterisolation using the present method.

In some examples, substantially purified 2-oxoglutarate can be obtainedin high concentrations by purifying L-glufosinate according to methodsdescribed herein. For example, using an aqueous solution of sodiumhydroxide and sodium chloride (e.g., an aqueous solution of 0.1 M NaOHand 1.5 M NaCl) as an eluent in a column chromatography method (e.g.,using anion exchange resin) can result in high concentrations ofsubstantially pure 2-oxoglutarate. 2-Oxoglutarate is a by-product of theamination of PPO and cannot be reused in the process described in the'254 application. The 2-oxoglutarate collected in the fractions exitingthe column can be converted to succinic acid by contacting the2-oxoglutarate with an excess of dilute hydrogen peroxide at roomtemperature. See, for example, A. Lopalco and V. J. Stella (2016) J.Pharm. Sci. 105:2879-2885, herein incorporated by reference.

Succinic acid is used in high volume as an ingredient in, or startingmaterial for, a wide range of commercial goods. Substantially purifiedsuccinic acid produced by this method can be purified further, ifdesired, concentrated and/or isolated by means known to those skilled inthe art. By substantially purified succinic acid or substantially puresuccinic acid it is intended that the amount of succinic acid in thefinal composition is 70% or greater, 75% or greater, 80% or greater, 85%or greater, 90% or greater, or 95% or greater than the sum of succinicacid, L-glufosinate, glutamate, 2-oxoglutarate, and pyroglutamate in thefinal composition.

In another embodiment, a cation exchange resin may be used to purifyL-glufosinate from pyroglutamic acid, 2-oxoglutarate, and PPO. In thisembodiment, the procedure can be carried out in two steps. In the firststep, the reaction mixture from the glutamic acid cyclization step canbe mixed with a cation exchange resin that has been converted to thehydrogen form using a suitable acid. Such acids include, but are notlimited to, concentrated hydrochloric acid, sulfuric acid, phosphoricacid, formic acid, acetic acid, trifluoroacetic acid, andmethanesulfonic acid. Similarly, the reaction mixture from the glutamicacid cyclization step is adjusted to an acidic pH, that is, a pH lessthan about 7.0 (e.g., a pH from about 0.5 to about 1.0, from about 1.0to about 2.0, from about 2.0 to about 3.0, from about 3.0 to about 4.0,from about 4.0 to about 5.0, from about 5.0 to about 6.0, or from about6.0 to about 6.9). Optionally, the reaction mixture from the glutamicacid cyclization step can be concentrated and/or decolorized asdescribed above prior to mixing with the cation resin. When mixed withthe resin, L-glufosinate and residual glutamic acid adsorb onto theresin while 2-oxoglutarate, PPO, and pyroglutamate do not. After asuitable period of time, the liquid containing the impurities can beseparated from the resin containing L-glufosinate. Optionally, after theadsorption of L-glufosinate is complete, the resin can be washed with asuitable liquid, such as water, which displaces residual solutioncontaining impurities without removing L-glufosinate from the resin.

In the second step, the resin containing L-glufosinate can be mixed witha water-soluble base which causes the L-glufosinate to desorb from theresin to form a solution of substantially purified L-glufosinate. Basessuitable for the removal of L-glufosinate from the cation resin includesodium hydroxide, potassium hydroxide, ammonium hydroxide,isopropylamine, ethanolamine, diethanolamine, and the like. Thisprocedure can be operated by contacting the resin and solution in batchmode as described above or in flow mode, wherein the resin is heldstationary in a container and the solutions are passed through it. Theprocedure can be carried out at a suitable temperature, for example,from about 20° C. to about 70° C. That is, a temperature in the range offrom about 25° C. to about 65° C., from about 30° C. to about 60° C., orfrom about 40° C. to about 50° C. The resin can be regenerated bycontacting it with a suitable acid, such hydrochloric acid, sulfuricacid, and the like, or a mixture of acid and an inorganic salt asdescribed above.

Many different types of commercially available cation exchange resinscan be used for the purification as described above. Suitable resins foruse as cation exchange resins can be constructed of a copolymer backbonewith various porosities, i.e., microporous or microporous. Gel typecation exchange resins are also suitable. Suitable resins can have auniform, Gaussian, or polydisperse particle size distribution. Thosehaving a bead shape and a uniform particle size distribution may bepreferred for the present method. The preferred mean volume averagediameter of resin particles used in the present method ranges from about10 microns to about 2000 microns, and a particularly useful range ofmedian diameter is from about 100 microns to about 1000 microns.

Resins can be converted to strong acid cation exchange resins bysubjecting the resin to a sulfonation reaction. Sulfonation occurs whenthe resins are contacted with various sulfonating agents such as sulfurtrioxide, concentrated sulfuric acid, chlorosulfonic acid, fumingsulfuric acid, and the like (see, U.S. Pat. Nos. 2,500,149; 2,527,300;and 2,597,439, all of which are incorporated herein by reference). Someresins, such as those including carboxylic acid monomers, can functionas weak acid cation resins (U.S. Pat. Nos. 4,062,817 and 4,614,751, bothof which are incorporated herein by reference). Cation exchange resinswith a cation capacity of from about 0.1 to about 4 milliequivalents pergram, wherein cation capacity is measured by ASTM D2187-94 (reapproved2004), are suitable for use in the present method. Examples of suitableresins include DOWEX™ 50WX8, DOWEX™ MONOSPHERE™ 99 K/350, DOWEX™MONOSPHERE™ C, DOWEX™ MARATHON™ MSC, as well as others known to thoseskilled in the art.

Those skilled in the art will recognize that multiple containerscontaining resin, such as those disclosed by U.S. Pat. No. 4,001,113,can be used for efficient operation of flow mode either in parallel orserial operation. Parallel operation allows for simultaneouspurification of the reaction mixture in several similar containers eachcontaining the ion exchange resin. In serial operation, partiallypurified L-glufosinate solution of undesired purity exiting a containerof resin is fed to a subsequent container which contains fresh orregenerated resin to continue the purification process. Immediatelyfollowing the feed of the partially purified L-glufosinate solution tothe subsequent container, the reaction mixture that has not been mixedwith resin is fed to the same container. In this way, the location ofthe reaction mixture moves to subsequent containers. This process isrepeated with other containers in series. In some examples, the usedresin is regenerated in some containers while partially purifiedL-glufosinate solution is fed to fresh or regenerated resin in othercontainers. This method is particularly suitable for continuousoperation.

Optionally, the volume of solution exiting the ion exchange step whichcontains substantially pure L-glufosinate can be contacted with awater-miscible organic solvent to cause the precipitation of inorganicsalts. Solvents which may be useful for this purpose include acetone,methanol, ethanol, 1-propanol, 2-propanol, acetonitrile,tetrahydrofuran, 1-methyl-2-propanol, 1,2-propanediol, and1,2-ethanediol. Methanol can be particularly useful in a number ofembodiments. In some embodiments, the volume of solution obtained fromthe ion exchange step is contacted with one or more volumes (e.g., fourvolumes) of methanol such that a sodium sulfate precipitate is formed.The precipitate, which contains very little L-glufosinate or noL-glufosinate, can be easily removed.

Chromatographic methods based on molecular size, known as size exclusionor gel filtration chromatography, may also be used to purifyL-glufosinate from the reaction mixture. In size exclusionchromatography, a solution is passed through a container containingresin with a particular pore size distribution. Without being bound toany particular theory, solutes too large to enter the pores of the resinpass through the container relatively quickly; these solutes areexcluded from moving into the resin particles. Solutes small enough toenter the pores will move into the resin particles and therefore willremain in the container for a longer period of time. Other factors inaddition to solute size, for example, solute structure, concentration,presence of salts, solution pH, etc., also may influence the degree ofseparation obtained. It is possible that the separation of solutes mayoccur by multiple modes of interaction with the resin, that is, acombination of size exclusion and either adsorption or ion exchange orboth. A description of the technique can be found in “Modern SizeExclusion Chromatography: Practice of Gel Permeation and GelFiltration”, second edition, A. M. Striegel, et al., John Wiley andSons, Inc., 2009; ISBN

The L-glufosinate mixture may be purified by passing the mixture througha container of suitable size exclusion resin. Components of the mixturethat are smaller in size and more compact in shape will have a longerresidence time within the container compared to L-glufosinate. All or aportion of the L-glufosinate in the mixture will elute from the columnbefore the other components, including inorganic salts, pyroglutamicacid and/or glutamic acid.

Resins useful for size exclusion chromatography can be prepared asdescribed above for ion exchange resins, with or withoutfunctionalization. U.S. Pat. Nos. 3,857,824 and 4,314,032 and Britishpatent GB1135302A disclose additional methods for preparing resin beadsfor size exclusion chromatography. Suitable resins are available on thecommercial scale from several manufacturers, including, but not limitedto, Toyopearl® HW-40, a product of Tosoh Bioscience; SEPABEADS™ SP825L,DIAION™ HP20SS and DIAION™ HP2MGL, products of Mitsubishi ChemicalCompany; and Sephadex® G-10, a product of GE Life Sciences.

The technique of simulated moving chromatography (“SMB”) can be used incombination with ion exchange resins or size exclusion resins to producesubstantially purified L-glufosinate. SMB is described in numerouspublications such as “Simulated Moving Bed Technology: Principles,Design and Process Applications”, A. Rodriguez; Butterworth-Heinemann,2015; ISBN:978-0128020241 and U.S. Pat. Nos. 2,985,589; 4,182,633;4,319,929; 4,412,866; 5,102,553; 7,229,558; and 7,931,751, all of whichare incorporated herein by reference. SMB operation efficiently utilizesresin and liquid streams, for example, the crude feed stream and eluentstream. Another advantage of SMB is that the method can be used for thecontinuous purification of the reaction mixture at a commercial scale.In the SMB technique, several containers are connected in series so asto form a continuous loop. Each container contains resin suited for theseparation of components. Valves and piping are connected to eachcontainer for the passage of at least four different types of fluids toand from each container; an example of a valve used for this purpose isdescribed in U.S. Pat. No. 6,431,202. These fluids are composed of themixture to be purified, an eluent, a substantially purified stream of afast-moving component or components and a substantially purified streamof a slow-moving component or components. The mixture to be purified andthe eluent are inputs to the process (meaning fed, individually, toseparate containers) while the fast-moving component(s) and slow-movingcomponent(s) are withdrawn from the process. The resin, eluent,temperature, and flowrates used in SMB are selected so that thesubstantially purified product is obtained either in the fast-movingcomponent stream or the slow-moving component stream. Without beingbound to any particular theory, the technique takes advantage of thedifferential interactions of the components in the mixture with theresin, which result in different rates of translation of the componentsthrough the continuous loop. As a result, the resin can be utilized withgreater efficiency and the volume of eluent can be minimized. In thesame manner, the method can be designed such that the L-glufosinate canbe the fast-moving component or the slow-moving component.

In one embodiment, SMB separation can be combined with a pretreatmentstep wherein one or more components of the mixture are removed bycontacting the mixture with an adsorbent prior to SMB operation. Suchcomponents removed include PPO, 2-oxoglutarate, and colored bodies.

In another embodiment, SMB separation is combined with a membraneseparation procedure as described previously. The membrane separationstep may be used to remove inorganic salts and/or water from thesolution, if desired. The membrane separation procedure can be practicedbefore or after the SMB separation.

The methods described herein remove approximately 80% or more (e.g.,about 85% or more, about 87% or more, or about 90% or more) of theunreacted glutamic acid as determined by ¹H-NMR, although HPLC and otheranalytical methods can also be used to determine percentages.

Substantially pure L-glufosinate is isolated by this method. Thus, themethod provides substantially pure compositions of L-glufosinate. Theform of the L-glufosinate can be crystalline, a liquid, an oil, or anamorphous solid. For example, the substantially pure compositions ofL-glufosinate includes material that is greater than 70% pureL-glufosinate or material that is contaminated with less than 30%D-glufosinate, PPO, 2-oxoglutarate, pyroglutamate, glutamate, or otherimpurities present in the starting materials, introduced during thereaction, during heating, or during cooling of the material, excludingwater; greater than 80% pure L-glufosinate or material that iscontaminated with less than 20% D-glufosinate, PPO, 2-oxoglutarate,pyroglutamate, glutamate, or other impurities present in the startingmaterials, introduced during the reaction, during heating, or duringcooling of the material, excluding water; greater than 85% pureL-glufosinate or material that is contaminated with less than 15%D-glufosinate, PPO, 2-oxoglutarate, pyroglutamate, glutamate, or otherimpurities present in the starting materials, introduced during thereaction, during heating, or during cooling of the material, excludingwater; greater than 90% pure L-glufosinate or material that iscontaminated with less than 10% D-glufosinate, PPO, 2-oxoglutarate,pyroglutamate, glutamate, or other impurities present in the startingmaterials, introduced during the reaction, during heating, or duringcooling of the material, excluding water; or greater than 95% pureL-glufosinate, or material that is contaminated with less than 5%D-glufosinate, PPO, 2-oxoglutarate, pyroglutamate, glutamate, or otherimpurities present in the starting materials, introduced during thereaction, during heating, or during cooling of the material, excludingwater.

In one embodiment, the volume of the solution exiting the ion exchangestep which contains substantially pure L-glufosinate can be reduced to aconcentrate that can be formulated directly into an herbicidal product.Any means of concentration known by those skilled in the art can beused, such as distillation (including distillation under vacuum), thinfilm evaporation, wiped film evaporation, as well as methods utilizing amembrane, such as pervaporation, reverse osmosis, nanofiltration,ultrafiltration, and the like. Water and solvents removed byconcentration can be recycled to the process, if desired.

In another embodiment, the concentrated L-glufosinate solution can beconcentrated further using any of the methods described above untilprecipitation or crystallization occurs. Optionally, a solvent orsolvent mixture can be added at any point in the process to assist withthe evaporation of water, to increase the purity of the solidL-glufosinate, to increase the yield of substantially purifiedL-glufosinate, or to modify the size and/or shape of the solidparticles. Solvents with a solubility in water of at least 10 wt. % areparticularly suitable for this purpose. Useful solvents include acetone,methanol, ethanol, 1-propanol, 2-propanol, acetonitrile,tetrahydrofuran, 1-methyl-2-propanol, 1,2-propanediol, 1,2-ethanediol,triethylamine, isopropylamine, and ammonium hydroxide. The solidmaterial produced by precipitation or crystallization can be filteredand dried to obtain a solid containing substantially pure L-glufosinate.If desired, the filtrate can be recycled back to the process. Anysuitable filtration equipment and drying equipment can be used for thispurpose. Water and solvent(s) removed by concentration can be recycledinto the process, if desired.

In another embodiment, the volume of solution exiting the ion exchangestep which contains substantially purified L-glufosinate can beconcentrated until precipitation or crystallization occurs, and thenevaporation of water and other volatile materials present can becontinued until a substantially dry solid is obtained. One advantage ofusing this process is that a filtration step is not required.Optionally, a solvent or solvent mixture can be added at any point toassist with the evaporation of water such as those solvents which forman azeotrope with water, including toluene, 1-butanol, t-amyl alcohol,and the like. Optionally, a component may be added to modify the sizeand/or shape of the solid particles, as described above. The solid,which contains substantially purified L-glufosinate, may be obtained asa powder, granular particles, large chunks, or mixtures thereof. Anysuitable equipment for carrying out this procedure may be used,including a rotary evaporator (rotovap), agitated pan dryer, horizontalaxis agitated dryer, and the like. Homogenization of the dried solid canbe performed, if desired. Water and solvent(s) removed during theprocess can be recycled, if desired.

In another embodiment, the volume of solution exiting the ion exchangestep which contains substantially purified L-glufosinate can betransferred to a spray dryer. The solution can be partially concentratedprior to being transferred to the spray dryer, and the partiallyconcentrated mixture can be in the form of a solution or, alternatively,if precipitation or crystallization has occurred, in the form of aslurry. The solid obtained after spray drying, which can be a powder ora granular form, contains substantially pure L-glufosinate. In anotherembodiment, agents which can improve the flowability of the driedparticles or other components can be mixed into the concentratedsolution or slurry prior to spray drying. In another embodiment, othermaterials such as formulation ingredients can be mixed into the solutionor partially concentrated mixture prior to spray drying.

II. Solid Forms

A number of solid forms of L-glufosinate, including crystalline formsand amorphous forms, are also provided herein.

In some embodiments, L-glufosinate ammonium Form A is provided. In someembodiments, Form A is characterized by an X-ray powder diffraction(XRPD) pattern including at least three peaks selected from 10.1, 10.8,16.8, 17.2, 18.3, 20.0, 20.2, 21.2, 21.5, 24.1, 24.3, 25.1, 25.6, 26.9,28.6, 29.0, 29.7, 29.9, 31.9, 33.4, 33.7, 34.5, 34.9, 35.4, 35.7, 36.1,36.7, 37.1, 37.5, 38.2, and 39.8° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation. For example, the XRPD pattern forForm A can include 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or 31 such peaks.

In some embodiments, Form A is characterized by an XRPD patternincluding at least six peaks selected from 10.1, 16.8, 18.3, 21.2, 24.1,24.3, 25.6, 26.9, 28.6, 29.0, and 34.5° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation. In some embodiments, Form A ischaracterized by an XRPD pattern including at least ten peaks selectedfrom 10.1, 16.8, 18.3, 21.2, 24.1, 24.3, 25.6, 26.9, 28.6, 29.0, and34.5° 2θ, ±0.2° 2θ, as determined on a diffractometer using Cu-Kαradiation. In some embodiments, Form A is characterized by an XRPDpattern which is substantially in accordance with FIG. 1 . As describedbelow, Form A has been analyzed by ion chromatography which indicated aglufosinate:ammonium ratio of approximately 1.4:1. In some embodiments,Form A is characterized by a differential scanning calorimetry (DSC)curve exhibiting an endotherm with an onset ranging from around 119 toaround 123° C. In some embodiments, the DSC curve is substantially inaccordance with the DSC curve depicted in FIG. 2 .

L-glufosinate ammonium Form A can be prepared according to methodsdescribed below. In some embodiments, preparation of L-glufosinateammonium Form A includes combining L-glufosinate ammonium with a polarsolvent (e.g., isopropanol or methanol), or a mixture of a polar solventand water; maintaining the resulting slurry at a temperature rangingfrom about 20° C. to about 50° C. for a period of time ranging from 1hour to 14 days; and isolating Form A from the slurry.

In some embodiments, L-glufosinate Form B is provided. In someembodiments, Form B is characterized by an X-ray powder diffraction(XRPD) pattern including at least three peaks selected from 10.0, 11.4,12.5, 16.5, 17.4, 18.1, 19.6, 20.0, 21.8, 22.9, 23.6, 24.0, 25.1, 25.5,26.1, 26.3, 26.4, 27.9, 28.2, 28.4, 28.7, 29.2, 30.2, 30.9, 31.6, 31.7,32.7, 33.0, 33.3, 34.3, 35.2, 36.7, 37.2, 37.4, 37.8, 38.3, 38.7, and39.3° 2θ, ±0.2° 2θ, as determined on a diffractometer using Cu-Kαradiation. For example, the XRPD pattern for Form B can include 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, or 38 such peaks.

In some embodiments, Form B is characterized by an XRPD patternincluding at least six peaks selected from 10.0, 12.5, 16.5, 17.4, 18.1,19.6, 20.0, 21.8, 22.9, 23.6, 24.0, 25.5, 26.3, 26.4, 29.2, 34.3, 35.2,and 37.4° 2θ, ±0.2° 2θ, as determined on a diffractometer using Cu-Kαradiation. In some embodiments, Form B is characterized by an XRPDpattern including at least ten peaks selected from 10.0, 12.5, 16.5,17.4, 18.1, 19.6, 20.0, 21.8, 22.9, 23.6, 24.0, 25.5, 26.3, 26.4, 29.2,34.3, 35.2, and 37.4° 2θ, ±0.2° 2θ, as determined on a diffractometerusing Cu-Kα radiation. In some embodiments, Form B is characterized byan XRPD pattern which is substantially in accordance with FIG. 3 . Asdescribed below, Form B has been analyzed by ion chromatography whichindicated a glufosinate:ammonium ratio of approximately 5.3:1. In someembodiments, Form B is characterized by a differential scanningcalorimetry (DSC) curve exhibiting an endotherm with an onset around123° C. In some embodiments, the DSC curve is substantially inaccordance with the DSC curve depicted in FIG. 4 .

L-glufosinate Form B can be prepared according to methods describedbelow. In some embodiments, preparation of L-glufosinate Form B includescombining L-glufosinate ammonium with a mixture of a polar solvent andwater; maintaining the resulting slurry at a temperature ranging fromabout 20° C. to about 50° C. for a period of time ranging from 1 hour to14 days; and isolating Form B from the slurry.

In some embodiments, L-glufosinate ammonium Form C is provided. In someembodiments, Form C is characterized by an X-ray powder diffraction(XRPD) pattern including at least three peaks selected from 9.1, 10.9,16.1, 16.8, 17.3, 18.3, 20.1, 21.4, 21.8, 22.4, 22.7, 24.1, 24.9, 25.4,25.6, 26.1, 26.6, 27.7, 28.3, 28.9, 30.8, 31.9, 32.6, 33.6, 33.9, 35.1,36.6, 37.1, 37.5, 38.3, 38.9, and 39.7° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation. For example, the XRPD pattern forForm C can include 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, or 34such peaks.

In some embodiments, Form C is characterized by an XRPD patternincluding at least six peaks selected from 9.1, 16.1, 16.8, 17.3, 21.8,24.1, 24.9, 25.6, 26.1, 28.3, and 28.9° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation. In some embodiments, Form C ischaracterized by an XRPD pattern including at least ten peaks selectedfrom 9.1, 16.1, 16.8, 17.3, 21.8, 24.1, 24.9, 25.6, 26.1, 28.3, and28.9° 2θ, ±0.2° 2θ, as determined on a diffractometer using Cu-Kαradiation. In some embodiments, Form C is characterized by an XRPDpattern which is substantially in accordance with FIG. 5 . As describedbelow, Form C has been analyzed by ion chromatography which indicated aglufosinate:ammonium ratio of approximately 1.4:1. In some embodiments,Form C is characterized by a differential scanning calorimetry (DSC)curve exhibiting an endotherm with an onset around 100° C. and/or anendotherm with an onset around 131° C. In some embodiments, the DSCcurve is substantially in accordance with the DSC curve depicted in FIG.6 .

L-glufosinate ammonium Form C can be prepared according to methodsdescribed below. In some embodiments, preparation of L-glufosinateammonium Form C includes contacting L-glufosinate ammonium with solventvapor (e.g., methanol vapor) at a temperature ranging from about 20° C.to about 30° C. for a period of time ranging from 1 hour to 14 days; andisolating Form C.

In some embodiments, L-glufosinate Form D is provided. In someembodiments, Form D is characterized by an X-ray powder diffraction(XRPD) pattern including at least three peaks selected from 9.1, 11.6,13.1, 14.1, 14.4, 16.2, 17.7, 18.2, 18.9, 19.3, 19.7, 21.2, 21.8, 22.4,23.2, 23.5, 25.3, 25.8, 26.2, 27.2, 28.6, 29.1, 30.0, 30.6, 31.1, 31.6,32.7, 33.5, 34.4, 34.7, 35.4, 35.9, 36.4, and 37.4° 2θ, ±0.2° 2θ, asdetermined on a diffractometer using Cu-Kα radiation. For example, theXRPD pattern for Form D can include 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,32, 33, or 34 such peaks.

In some embodiments, Form D is characterized by an XRPD patternincluding at least six peaks selected from 9.1, 17.7, 18.2, 18.9, 22.4,23.2, 23.5, 26.2, 33.5, and 36.4° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation. In some embodiments, Form D ischaracterized by an XRPD pattern including peaks at 9.1, 17.7, 18.2,18.9, 22.4, 23.2, 23.5, 26.2, 33.5, and 36.4° 2θ, ±0.2° 2θ, asdetermined on a diffractometer using Cu-Kα radiation. In someembodiments, Form D is characterized by an XRPD pattern which issubstantially in accordance with FIG. 7 . As described below, Form D hasbeen analyzed by ion chromatography which indicated aglufosinate:ammonium ratio of approximately 3.9:1. In some embodiments,Form D is characterized by a differential scanning calorimetry (DSC)curve exhibiting a broad endotherm with an onset around 140° C. In someembodiments, the DSC curve is substantially in accordance with the DSCcurve depicted in FIG. 8 .

L-glufosinate Form D can be prepared according to methods describedbelow. In some embodiments, preparation of L-glufosinate Form D includescombining L-glufosinate ammonium with a mixture of solvent (e.g.,methanol, ethanol, trifluoroethanol, isopropanol, acetone, dimethylacetamide, or the like, which are optionally anhydrous); maintaining theresulting slurry at a temperature ranging from about 50° C. to about 60°C. for a period of time ranging from 1 hour to 14 days; and isolatingForm D from the slurry.

In some embodiments, L-glufosinate hydrochloride Form E is provided. Insome embodiments, Form E is characterized by an X-ray powder diffraction(XRPD) pattern including at least three peaks selected from 13.1, 16.8,18.2, 19.4, 20.5, 20.9, 21.4, 22.5, 23.4, 25.3, 26.2, 26.5, 26.9, 27.8,28.1, 30.2, 31.2, 31.5, 32.3, 33.8, 34.4, 35.3, 35.7, 36.3, 36.9, 37.8,38.2, 38.8, and 39.4° 2θ, ±0.2° 2θ, as determined on a diffractometerusing Cu-Kα radiation. For example, the XRPD pattern for Form E caninclude 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31 such peaks.

In some embodiments, Form E is characterized by an XRPD patternincluding at least six peaks selected from 16.8, 18.2, 20.5, 21.4, 22.5,22.9, 23.4, 25.3, 30.2, and 31.2° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation. In some embodiments, Form E ischaracterized by an XRPD pattern including peaks at least ten peaksselected from 16.8, 18.2, 20.5, 21.4, 22.5, 22.9, 23.4, 25.3, 30.2, and31.2° 2θ, ±0.2° 2θ, as determined on a diffractometer using Cu-Kαradiation. In some embodiments, Form E is characterized by an XRPDpattern which is substantially in accordance with FIG. 9 . As describedbelow, Form E has been analyzed by ion chromatography which indicated astoichiometric amount of L-glufosinate and chloride.

L-glufosinate hydrochloride Form E can be prepared according to methodsdescribed below. In some embodiments, preparation of L-glufosinatehydrochloride Form E includes combining L-glufosinate ammonium withwater and hydrochloride acid; adding a solvent (e.g., methanol, ethanol,trifluoroethanol, isopropanol, acetone, dimethyl acetamide, or the like)to the resulting mixture; maintaining the mixture at a temperatureranging from about 20° C. to about 30° C. for a period of time rangingfrom 1 hour to 14 days; and isolating Form E from the mixture.

III. Compositions

Also described herein are compositions including the L-glufosinatedescribed above. In some embodiments, the composition substantiallyincludes L-glufosinate and an acceptable cationic or anionic salt formssuch as the sodium, potassium, hydrochloride, sulfate, ammonium, orisopropylammonium salts. The composition may additionally comprise amixture of L-glufosinate, PPO, and D-glufosinate, where L-glufosinate isthe predominate compound. In other words, L-glufosinate is present inthe composition in an amount greater than about 50 wt. % (e.g., greaterthan about 55 wt. %, greater than about 60 wt. %, greater than about 65wt. %, greater than about 70 wt. %, greater than about 75 wt. %, greaterthan about 80 wt. %, greater than about 85 wt. %, greater than about 90wt. %, or greater than about 95 wt. %).

The purified L-glufosinate described herein can be used in compositionsuseful for application to a field of crop plants for the prevention orcontrol of weeds. The composition may be formulated as a liquid forspraying on a field. The L-glufosinate is provided in the composition ineffective amounts. As used herein, effective amount means from about 10grams active ingredient per hectare to about 1,500 grams activeingredient per hectare, e.g., from about 50 grams to about 400 grams orfrom about 100 grams to about 350 grams. In some embodiments, the activeingredient is L-glufosinate. For example, the amount of L-glufosinate inthe composition can be about 10 grams, about 50 grams, about 100 grams,about 150 grams, about 200 grams, about 250 grams, about 300 grams,about 350 grams, about 400 grams, about 450 grams, about 500 grams,about 550 grams, about 600 grams, about 650 grams, about 700 grams,about 750 grams, about 800 grams, about 850 grams, about 900 grams,about 950 grams, about 1,000 grams, about 1,050 grams, about 1,100grams, about 1,150 grams, about 1,200 grams, about 1,250 grams, about1,300 grams, about 1,350 grams, about 1,400 grams, about 1,450 grams, orabout 1,500 grams L-glufosinate per hectare.

The herbicidal compositions (including concentrates which requiredilution prior to application to the plants) described herein containL-glufosinate (i.e., the active ingredient), optionally some residualD-glufosinate and/or PPO, and one or more adjuvant components in liquidor solid form.

The compositions are prepared by admixing the active ingredient with oneor more adjuvants, such as diluents, extenders, carriers, surfactants,organic solvents, humectants, or conditioning agents, to provide acomposition in the form of a finely-divided particulate solid, pellet,solution, dispersion, or emulsion. Thus, the active ingredient can beused with an adjuvant, such as a finely-divided solid, a liquid oforganic origin, water, a wetting agent, a dispersing agent, anemulsifying agent, or any suitable combination of these. From theviewpoint of economy and convenience, water is the preferred diluent.However, not all the compounds are resistant to hydrolysis and in somecases this may dictate the use of non-aqueous solvent media, asunderstood by those of skill in the art.

Optionally, one or more additional components can be added to thecomposition to produce a formulated herbicidal composition. Suchformulated compositions can include L-glufosinate, carriers (e.g.,diluents and/or solvents), and other components. The formulatedcomposition includes an effective amount of L-glufosinate. Optionally,the L-glufosinate can be present in the form of L-glufosinate ammonium.The L-glufosinate ammonium can be present in an amount ranging from 10%to 30% by weight of the formulated composition. For example, theL-glufosinate ammonium can be present in an amount of 10%, 12%, 14%,16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30% by weight of the formulatedcomposition. Optionally, the L-glufosinate ammonium is present in anamount of 12.25% or 24.5% by weight of the formulated composition.

In some examples, the formulated composition can include one or moresurfactants. A suitable surfactant for use in the formulated compositionincludes sodium alkyl ether sulfate. The surfactant can be present in anamount from 10% to 40% by weight of the formulated composition. Forexample, the surfactant can be present in an amount of 10%, 12%, 14%,16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40% byweight of the formulated composition. Optionally, the sodium alkyl ethersulfate is present in an amount of 11.05%, 15.8%, 22.1%, or 31.6% byweight of the formulated composition.

The formulated composition can optionally include one or more solvents(e.g., organic solvents). Optionally, the solvent can be1-methoxy-2-propanol, dipropylene glycol, ethylene glycol, and mixturesthereof. The one or more solvents can be present in an amount rangingfrom 0.5% to 20% by weight of the formulated composition. For example,the total amount of solvents in the composition can be present in anamount of 0.5% to 18%, 5% to 15%, or 7.5% to 10% by weight of theformulated composition.

Optionally, the solvent includes a combination of two solvents. Forexample, the solvents in the formulation can include1-methoxy-2-propanol and dipropylene glycol. The 1-methoxy-2-propanolcan be present, for example, in an amount of 0.5% to 2% by weight of theformulated composition. For example, the 1-methoxy-2-propanol can bepresent in the amount of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%,1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0% by weight of theformulated composition. Optionally, the 1-methoxy-2-propanol is presentin an amount of 0.5% or 1.0% by weight of the formulated composition.The dipropylene glycol can be present in an amount of from 4% to 18% byweight of the formulated composition. For example, the dipropyleneglycol can be present in an amount of 4%, 6%, 8%, 10%, 12%, 14%, 16%, or18% by weight of the formulated composition. Optionally, the dipropyleneglycol is present in an amount of 4.3% or 8.6% by weight of theformulated composition.

The formulated composition can also include one or more polysaccharidehumectants. Examples of suitable polysaccharide humectants include, forexample, alkyl polysaccharides, pentoses, high fructose corn syrup,sorbitol, and molasses. The polysaccharide humectant, such as alkylpolysaccharide, can be present in the formulated composition in anamount ranging from 4% to 20% by weight of the formulated composition.For example, the total amount of polysaccharide humectant in thecomposition can be from 4% to 18%, 4.5% to 15%, or 5% to 10% by weightof the formulated composition. In some examples, the total amount ofpolysaccharide humectant, such as the alkyl polysaccharide, present inthe formulated composition can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%,13%, 14%, 15%, 16%, 17%, or 18%. Optionally, the alkyl polysaccharidecan be present in an amount of 3.2%, 4.9%, 6.2%, or 9.8% by weight ofthe formulated composition.

A diluent can also be included in the formulated composition. Suitablediluents include water and other aqueous components. Optionally, thediluents are present in an amount necessary to produce compositionsready for packaging or for use.

In one example, the formulated composition includes L-glufosinateammonium in an amount of 12.25% by weight of the formulation; sodiumalkyl ether sulfate in an amount of 31.6% by weight of the formulation;1-methoxy-2-propanol in an amount of 1% by weight of the formulation;dipropylene glycol in an amount of 8.6% by weight of the formulation;alkyl polysaccharide in an amount of 9.8% by weight of the formulation;and water. In some embodiments, the formulated composition includeswater in an amount of 36.75% by weight of the formulation.

In another example, the formulated composition includes L-glufosinateammonium in an amount of 24.5% by weight of the formulation; sodiumalkyl ether sulfate in an amount of 31.6% by weight of the formulation;1-methoxy-2-propanol in an amount of 1% by weight of the formulation;dipropylene glycol in an amount of 8.6% by weight of the formulation;alkyl polysaccharide in an amount of 9.8% by weight of the formulation;and water. In some embodiments, the formulated composition includeswater in an amount of 36.75% by weight of the formulation.

In another example, the formulated composition includes L-glufosinateammonium in an amount of 12.25% by weight of the formulation; sodiumalkyl ether sulfate in an amount of 15.8% by weight of the formulation;1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation;dipropylene glycol in an amount of 4.3% by weight of the formulation;alkyl polysaccharide in an amount of 4.9% by weight of the formulation;and water. In some embodiments, the formulated composition includeswater in an amount of 62.25% by weight of the formulation.

In another example, the formulated composition includes L-glufosinateammonium in an amount of 24.5% by weight of the formulation; sodiumalkyl ether sulfate in an amount of 22.1% by weight of the formulation;1-methoxy-2-propanol in an amount of 1% by weight of the formulation;alkyl polysaccharide in an amount of 6.2% by weight of the formulation;and water. In some embodiments, the formulated composition includeswater in an amount of 46.2% by weight of the formulation.

In another example, the formulated composition includes L-glufosinateammonium in an amount of 12.25% by weight of the formulation; sodiumalkyl ether sulfate in an amount of 22.1% by weight of the formulation;1-methoxy-2-propanol in an amount of 1% by weight of the formulation;alkyl polysaccharide in an amount of 6.2% by weight of the formulation;and water. In some embodiments, the formulated composition includeswater in an amount of 58.45% by weight of the formulation.

In another example, the formulated composition includes L-glufosinateammonium in an amount of 12.25% by weight of the formulation; sodiumalkyl ether sulfate in an amount of 11.05% by weight of the formulation;1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation;alkyl polysaccharide in an amount of 3.1% by weight of the formulation;and water. In some embodiments, the formulated composition includeswater in an amount of 73.1% by weight of the formulation.

The total amount of water may vary and will depend, in part, on thenumber and quantity of other components in the formulated compositions.Further components suitable for use in the formulated compositionsprovided herein are described in U.S. Pat. Nos. 4,692,181 and 5,258,358,both of which are incorporated by reference herein in their entireties.

The formulated compositions described herein, particularly liquids andsoluble powders, can contain as further adjuvant components one or moresurface-active agents in amounts sufficient to render a givencomposition readily dispersible in water or in oil. The incorporation ofa surface-active agent into the compositions greatly enhances theirefficacy. Surface-active agents, as used herein, include wetting agents,dispersing agents, suspending agents, and emulsifying agents. Anionic,cationic, and non-ionic agents can be used with equal facility.

Suitable wetting agents include alkyl benzene and alkyl naphthalenesulfonates, sulfated fatty alcohols, amines or acid amides, long chainacid esters of sodium isothionate, esters of sodium sulfosuccinate,sulfated or sulfonated fatty acid esters petroleum sulfonates,sulfonated vegetable oils, ditertiary acetylenic glycols,polyoxyethylene derivatives of alkylphenols (particularly isooctylphenoland nonylphenol), and polyoxyethylene derivatives of the mono-higherfatty acid esters of hexitol anhydrides (e.g., sorbitan). Exemplarydispersants include methyl cellulose, polyvinyl alcohol, sodium ligninsulfonates, polymeric alkyl naphthalene sulfonates, sodium naphthalenesulfonate, polymethylene bisnaphthalenesulfonate, and sodiumN-methyl-N-(long chain acid) laurates.

Water-dispersible powder compositions can be made containing one or moreactive ingredients, an inert solid extender, and one or more wetting anddispersing agents. The inert solid extenders are usually of mineralorigin, such as the natural clays, diatomaceous earth, and syntheticminerals derived from silica and the like. Examples of such extendersinclude kaolinites, attapulgite clay, and synthetic magnesium silicate.Water-dispersible powders described herein can optionally contain fromabout 5 to about 95 parts by weight of active ingredient (e.g., fromabout 15 to 30 parts by weight of active ingredient), from about 0.25 to25 parts by weight of wetting agent, from about 0.25 to 25 parts byweight of dispersant, and from 4.5 to about 94.5 parts by weight ofinert solid extender, all parts being by weight of the totalcomposition. Where required, from about 0.1 to 2.0 parts by weight ofthe solid inert extender can be replaced by a corrosion inhibitor oranti-foaming agent or both.

Aqueous suspensions can be prepared by dissolution or by mixing togetherand grinding an aqueous slurry of a water-insoluble active ingredient inthe presence of a dispersing agent to obtain a concentrated slurry ofvery finely-divided particles. The resulting concentrated aqueoussuspension is characterized by its extremely small particle size, sothat when diluted and sprayed, coverage is very uniform.

Emulsifiable oils are usually solutions of active ingredients inwater-immiscible or partially water-immiscible solvents together with asurface active agent. Suitable solvents for the active ingredientdescribed herein include hydrocarbons and water-immiscible ethers,esters, or ketones. The emulsifiable oil compositions generally containfrom about 5 to 95 parts active ingredient, about 1 to 50 parts surfaceactive agent, and about 4 to 94 parts solvent, all parts being by weightbased on the total weight of emulsifiable oil.

The formulated compositions described herein can also contain otheradditives, for example, fertilizers, phytotoxicants and plant growthregulators, pesticides, and the like used as adjuvants or in combinationwith any of the above-described adjuvants. The formulated compositionsdescribed herein can also be admixed with the other materials, e.g.,fertilizers, other phytotoxicants, etc., and applied in a singleapplication.

In each of the formulation types described herein, e.g., liquid andsolid formulations, the concentration of the active ingredients can bethe same.

In some embodiments, the composition can include 2-oxoglutarate as amajor component. 2-oxoglutarate is an important dicarboxylic acid andone of the key intermediates in the tricarboxylic acid cycle and aminoacid metabolism. 2-oxoglutarate can be isolated from the reactionmixture by methods such as that set forth in French Patent No. 07199,herein incorporated by reference. The 2-oxoglutarate composition can beformulated with pharmaceutical excipients and carriers, food additives,or components used to form biomaterials. The 2-oxoglutarate compositioncan be used in a variety of applications, including in synthesizingpharmaceutical agents, food additives, and biomaterials, as described inLi et al., Bioprocess Biosyst Eng, 39:967-976 (2016).

It is recognized that the formulated herbicidal compositions can be usedin combination with other herbicides. The herbicidal compositionsdescribed herein are often applied in conjunction with one or more otherherbicides to control a wider variety of undesirable vegetation. Whenused in conjunction with other herbicides, the presently claimedcompounds can be formulated with the other herbicide or herbicides, tankmixed with the other herbicide or herbicides, or applied sequentiallywith the other herbicide or herbicides. Some of the herbicides that canbe employed in conjunction with the formulated herbicidal compositionsdescribed herein include: amide herbicides such as allidochlor,6-arylpicolinates, beflubutamid, benzadox, benzipram, bromobutide,cafenstrole, CDEA, chlorthiamid, 6-cyclopropylpicolinates, cyprazole,dimethenamid, dimethenamid-P, diphenamid, epronaz, etnipromid,fentrazamide, flupoxam, fomesafen, halo safen, isocarbamid, isoxaben,napropamide, naptalam, pethoxamid, propyzamide, quinonamid and tebutam;anilide herbicides such as chloranocryl, cisanilide, clomeprop,cypromid, diflufenican, etobenzanid, fenasulam, flufenacet, flufenican,mefenacet, mefluidide, metamifop, monalide, naproanilide, pentanochlor,picolinafen and propanil; arylalanine herbicides such as benzoylprop,flamprop and flamprop-M; chloroacetanilide herbicides such asacetochlor, alachlor, butachlor, butenachlor, delachlor, diethatyl,dimethachlor, metazachlor, metolachlor, S-metolachlor, pretilachlor,propachlor, propisochlor, prynachlor, terbuchlor, thenylchlor andxylachlor; sulfonanilide herbicides such as benzofluor, perfluidone,pyrimisulfan and profluazol; sulfonamide herbicides such as asulam,carbasulam, fenasulam and oryzalin; antibiotic herbicides such asbilanafos; benzoic acid herbicides such as chloramben, dicamba,2,3,6-TBA and tricamba; pyrimidinyloxybenzoic acid herbicides such asbispyribac and pyriminobac; pyrimidinylthiobenzoic acid herbicides suchas pyrithiobac; phthalic acid herbicides such as chlorthal; picolinicacid herbicides such as aminopyralid, clopyralid and picloram;quinolinecarboxylic acid herbicides such as quinclorac and quinmerac;arsenical herbicides such as cacodylic acid, CMA, DSMA, hexaflurate,MAA, MAMA, MSMA, potassium arsenite and sodium arsenite;benzoylcyclohexanedione herbicides such as mesotrione, sulcotrione,tefuryltrione and tembotrione; benzofuranyl alkylsulfonate herbicidessuch as benfuresate and ethofumesate; carbamate herbicides such asasulam, carboxazole chlorprocarb, dichlormate, fenasulam, karbutilateand terbucarb; carbanilate herbicides such as barban, BCPC, carbasulam,carbetamide, CEPC, chlorbufam, chlorpropham, CPPC, desmedipham,phenisopham, phenmedipham, phenmedipham-ethyl, propham and swep;cyclohexene oxime herbicides such as alloxydim, butroxydim, clethodim,cloproxydim, cycloxydim, profoxydim, sethoxydim, tepraloxydim andtralkoxydim; cyclopropylisoxazole herbicides such as isoxachlortole andisoxaflutole; dicarboximide herbicides such as benzfendizone,cinidon-ethyl, flumezin, flumiclorac, flumioxazin and flumipropyn;dinitroaniline herbicides such as benfluralin, butralin, dinitramine,ethalfluralin, fluchloralin, isopropalin, methalpropalin, nitralin,oryzalin, pendimethalin, prodiamine, profluralin and trifluralin;dinitrophenol herbicides such as dinofenate, dinoprop, dinosam, dinoseb,dinoterb, DNOC, etinofen and medinoterb; diphenyl ether herbicides suchas ethoxyfen; nitrophenyl ether herbicides such as acifluorfen,aclonifen, bifenox, chlomethoxyfen, chlomitrofen, etnipromid,fluorodifen, fluoroglycofen, fluoronitrofen, fomesafen, furyloxyfen,halosafen, lactofen, nitrofen, nitrofluorfen and oxyfluorfen;dithiocarbamate herbicides such as dazomet and metam; halogenatedaliphatic herbicides such as alorac, chloropon, dalapon, flupropanate,hexachloroacetone, iodomethane, methyl bromide, monochloroacetic acid,SMA and TCA; imidazolinone herbicides such as imazamethabenz, imazamox,imazapic, imazapyr, imazaquin and imazethapyr; inorganic herbicides suchas ammonium sulfamate, borax, calcium chlorate, copper sulfate, ferroussulfate, potassium azide, potassium cyanate, sodium azide, sodiumchlorate and sulfuric acid; nitrile herbicides such as bromobonil,bromoxynil, chloroxynil, dichlobenil, iodobonil, ioxynil and pyraclonil;organophosphorus herbicides such as amiprofos-methyl, anilofos,bensulide, bilanafos, butamifos, 2,4-DEP, DMPA, EBEP, fosamine,glyphosate and piperophos; phenoxy herbicides such as bromofenoxim,clomeprop, 2,4-DEB, 2,4-DEP, difenopenten, disul, erbon, etnipromid,fenteracol and trifopsime; phenoxyacetic herbicides such as 4-CPA,2,4-D, 3,4-DA, MCPA, MCPA-thioethyl and 2,4,5-T; phenoxybutyricherbicides such as 4-CPB, 2,4-DB, 3,4-DB, MCPB and 2,4,5-TB;phenoxypropionic herbicides such as cloprop, 4-CPP, dichlorprop,dichlorprop-P, 3,4-DP, fenoprop, mecoprop and mecoprop-P;aryloxyphenoxypropionic herbicides such as chlorazifop, clodinafop,clofop, cyhalofop, diclofop, fenoxaprop, fenoxaprop-P, fenthiaprop,fluazifop, fluazifop-P, haloxyfop, haloxyfop-P, isoxapyrifop, metamifop,propaquizafop, quizalofop, quizalofop-P and trifop; phenylenediamineherbicides such as dinitramine and prodiamine; pyrazolyl herbicides suchas benzofenap, pyrazolynate, pyrasulfotole, pyrazoxyfen, pyroxasulfoneand topramezone; pyrazolylphenyl herbicides such as fluazolate andpyraflufen; pyridazine herbicides such as credazine, pyridafol andpyridate; pyridazinone herbicides such as brompyrazon, chloridazon,dimidazon, flufenpyr, metflurazon, norflurazon, oxapyrazon and pydanon;pyridine herbicides such as aminopyralid, cliodinate, clopyralid,dithiopyr, fluroxypyr, haloxydine, picloram, picolinafen, pyriclor,thiazopyr and triclopyr; pyrimidinediamine herbicides such as iprymidamand tioclorim; quaternary ammonium herbicides such as cyperquat,diethamquat, difenzoquat, diquat, morfamquat and paraquat; thiocarbamateherbicides such as butylate, cycloate, di-allate, EPTC, esprocarb,ethiolate, isopolinate, methiobencarb, molinate, orbencarb, pebulate,prosulfocarb, pyributicarb, sulfallate, thiobencarb, tiocarbazil,tri-allate and vemolate; thiocarbonate herbicides such as dimexano, EXDand proxan; thiourea herbicides such as methiuron; triazine herbicidessuch as dipropetryn, triaziflam and trihydroxytriazine; chlorotriazineherbicides such as atrazine, chlorazine, cyanazine, cyprazine,eglinazine, ipazine, mesoprazine, procyazine, proglinazine, propazine,sebuthylazine, simazine, terbuthylazine and trietazine; methoxytriazineherbicides such as atraton, methometon, prometon, secbumeton, simetonand terbumeton; methylthiotriazine herbicides such as ametryn,aziprotryne, cyanatryn, desmetryn, dimethametryn, methoprotryne,prometryn, simetryn and terbutryn; triazinone herbicides such asametridione, amibuzin, hexazinone, isomethiozin, metamitron andmetribuzin; triazole herbicides such as amitrole, cafenstrole, epronazand flupoxam; triazolone herbicides such as amicarbazone, bencarbazone,carfentrazone, flucarbazone, propoxycarbazone, sulfentrazone andthiencarbazone-methyl; triazolopyrimidine herbicides such ascloransulam, diclosulam, florasulam, flumetsulam, metosulam, penoxsulamand pyroxsulam; uracil herbicides such as butafenacil, bromacil,flupropacil, isocil, lenacil and terbacil; 3-phenyluracils; ureaherbicides such as benzthiazuron, cumyluron, cycluron, dichloralurea,diflufenzopyr, isonoruron, isouron, methabenzthiazuron, monisouron andnoruron; phenylurea herbicides such as anisuron, buturon, chlorbromuron,chloreturon, chlorotoluron, chloroxuron, daimuron, difenoxuron,dimefuron, diuron, fenuron, fluometuron, fluothiuron, isoproturon,linuron, methiuron, methyldymron, metobenzuron, metobromuron, metoxuron,monolinuron, monuron, neburon, parafluron, phenobenzuron, siduron,tetrafluron and thidiazuron; pyrimidinylsulfonylurea herbicides such asamidosulfuron, azimsulfuron, bensulfuron, chlorimuron, cyclosulfamuron,ethoxysulfuron, flazasulfuron, flucetosulfuron, flupyrsulfuron,foramsulfuron, halosulfuron, imazosulfuron, mesosulfuron, nicosulfuron,orthosulfamuron, oxasulfuron, primisulfuron, pyrazosulfuron,rimsulfuron, sulfometuron, sulfosulfuron and trifloxysulfuron;triazinylsulfonylurea herbicides such as chlorsulfuron, cinosulfuron,ethametsulfuron, iodosulfuron, metsulfuron, prosulfuron, thifensulfuron,triasulfuron, tribenuron, triflusulfuron and tritosulfuron;thiadiazolylurea herbicides such as buthiuron, ethidimuron, tebuthiuron,thiazafluron and thidiazuron; and unclassified herbicides such asacrolein, allyl alcohol, aminocyclopyrachlor, azafenidin, benazolin,bentazone, benzobicyclon, buthidazole, calcium cyanamide, cambendichlor,chlorfenac, chlorfenprop, chlorflurazole, chlorflurenol, cinmethylin,clomazone, CPMF, cresol, ortho-dichlorobenzene, dimepiperate, endothal,fluoromidine, fluridone, flurochloridone, flurtamone, fluthiacet,indanofan, methazole, methyl isothiocyanate, nipyraclofen, OCH,oxadiargyl, oxadiazon, oxaziclomefone, pentachlorophenol, pentoxazone,phenylmercury acetate, pinoxaden, prosulfalin, pyribenzoxim, pyriftalid,quinoclamine, rhodethanil, sulglycapin, thidiazimin, tridiphane,trimeturon, tripropindan and tritac. The herbicidal compositions of thepresent invention can, further, be used in conjunction with glyphosate,dicamba, or 2,4-D on glyphosate-tolerant, dicamba-tolerant, or2,4-D-tolerant crops. It is generally preferred to use the compositionsdescribed herein in combination with herbicides that are selective forthe crop being treated and which complement the spectrum of weedscontrolled by these compositions at the application rate employed. It isfurther generally preferred to apply the compositions described hereinand other complementary herbicides at the same time, either as acombination formulation or as a tank mix.

IV. Methods of Using

The compositions described herein can be used in methods for selectivelycontrolling weeds in a field or any other area, including, for example,a railway, lawn, golf course, and others where the control of weeds isdesired. Optionally, the field or other area can contain a crop ofplanted seeds or crops that are resistant to glufosinate. The methodscan include applying an effective amount of a composition comprisingL-glufosinate as described herein to the field.

The compositions described herein are useful for application to a fieldof crop plants for the prevention or control of weeds. The compositionsmay be formulated as a liquid for spraying on a field. The L-glufosinateis provided in the compositions in effective amounts. As used herein,effective amount means from about 10 grams active ingredient per hectareto about 1,500 grams active ingredient per hectare, e.g., from about 50grams to about 400 grams or from about 100 grams to about 350 grams. Insome embodiments, the active ingredient is L-glufosinate. For example,the amount of L-glufosinate in the composition can be about 10 grams,about 50 grams, about 100 grams, about 150 grams, about 200 grams, about250 grams, about 300 grams, about 350 grams, about 400 grams, about 500grams, about 550 grams, about 600 grams, about 650 grams, about 700grams, about 750 grams, about 800 grams, about 850 grams, about 900grams, about 950 grams, about 1,000 grams, about 1,050 grams, about1,100 grams, about 1,150 grams, about 1,200 grams, about 1,250 grams,about 1,300 grams, about 1,350 grams, about 1,400 grams, about 1,450grams, or about 1,500 grams L-glufosinate per hectare.

V. Exemplary Embodiments

Non-limiting embodiments include:

1. A method for purifying L-glufosinate from a composition comprisingL-glufosinate and glutamate, by converting the glutamate topyroglutamate to facilitate isolation of L-glufosinate, said methodcomprising:

-   -   reacting an L-glufosinate composition comprising L-glufosinate        and glutamate at an elevated temperature for a sufficient period        of time to convert the majority of glutamate to pyroglutamate;        and,    -   isolating L-glufosinate from the pyroglutamate and other        components of the composition to obtain a composition of        substantially purified L-glufosinate (90% or greater of the sum        of L-glufosinate, glutamate, and pyroglutamate).        2. The method of embodiment 1, wherein a portion of the initial        glutamate in the composition is first separated from the        L-glufosinate by crystallization and filtration followed by        conversion of glutamate to pyroglutamate.        3. The method of embodiment 2, wherein the separated glutamate        is recycled to the enzymatic reaction combining a D-amino acid        oxidase and a transaminase.        4. The method of embodiment 1, wherein the isolation of        L-glufosinate from pyroglutamate is performed using ion        exchange.        5. The method of embodiment 4, further comprising contacting the        L-glufosinate isolated using ion exchange with methanol to        precipitate inorganic salts.        6. The method of embodiment 1, wherein the isolation of        L-glufosinate from pyroglutamate is performed using size        exclusion chromatography.        7. The method of embodiment 1, wherein the elevated temperature        comprises a temperature of from 120° C. to 180° C.        8. The method of embodiment 1, wherein the sufficient period of        time comprises at least 2 hours.        9. The method of embodiment 8, wherein the sufficient period of        time comprises from 2 hours to 18 hours.        10. A method for purifying L-glufosinate, comprising converting        excess glutamate to pyroglutamate to facilitate isolation of        L-glufosinate, said method comprising:    -   reacting an L-glufosinate composition comprising L-glufosinate        and glutamate in the presence of a glutaminyl-peptide        cyclotransferase for a sufficient period of time to convert the        majority of glutamate to pyroglutamate; and,    -   isolating L-glufosinate from the pyroglutamate and other        components of the composition to obtain a composition of        substantially purified L-glufosinate (90% or greater of the sum        of L-glufosinate, glutamate, and pyroglutamate).        11. The method of embodiment 10, wherein the sufficient period        of time comprises at least 2 hours.        12. The method of embodiment 11, wherein the sufficient period        of time comprises from 2 hours to 18 hours.        13. The method of embodiment 10, wherein the isolation of        L-glufosinate from pyroglutamate is performed using ion        exchange.        14. The method of embodiment 13, further comprising contacting        the L-glufosinate isolated using ion exchange with methanol to        precipitate inorganic salts.        15. The method of embodiment 10, wherein the isolation of        L-glufosinate from pyroglutamate is performed using size        exclusion chromatography.        16. A method for obtaining purified succinic acid as a        by-product from a method of making L-glufosinate, said method        comprising:    -   aminating PPO to L-glufosinate by a transaminase (TA) enzyme,        using an amine group from glutamic acid present in the        composition, thereby generating a 2-oxoglutaric acid by-product;    -   reacting an L-glufosinate composition comprising L-glufosinate,        glutamate, and 2-oxoglutaric acid at an elevated temperature for        a sufficient period of time to convert the majority of glutamate        to pyroglutamate;    -   isolating 2-oxoglutaric acid from the composition by ion        exchange to obtain a composition of substantially purified        2-oxoglutaric acid; and    -   contacting the substantially purified 2-oxoglutaric acid with        hydrogen peroxide to obtain a composition of substantially        purified succinic acid.        17. The method of embodiment 10 or 16, wherein a portion of the        initial glutamate in the composition is first separated from the        L-glufosinate by crystallization and filtration followed by        conversion of glutamate to pyroglutamate.        18. The method of embodiment 17, wherein acid is added to        crystallize glutamate.        19. The method of embodiment 18, wherein said acid is selected        from the group consisting of sulfuric acid, hydrochloric acid,        phosphoric acid, formic acid, and acetic acid.        20. The method of embodiment 18, wherein the composition is        heated to an elevated temperature before, during, or after the        addition of said acid.        21. The method of embodiment 20, wherein said elevated        temperature ranges from about 35° C. to about 90° C.        22. The method of embodiment 20, wherein said elevated        temperature ranges from about 40° C. to about 80° C.        23. The method of embodiment 20, wherein said elevated        temperature ranges from about 50° C. to about 70° C.        24. The method of embodiment 20, wherein the composition is        cooled to a temperature below 25° C. after heating.        25. The method of embodiment 24, wherein said temperature ranges        from about −5° C. to about 15° C.        26. The method of embodiment 24, wherein said temperature ranges        from about 0° C. to about 10° C.        27. The method of embodiment 17, wherein the separated glutamate        is recycled to the enzymatic reaction combining a D-amino acid        oxidase and a transaminase.        28. The method of embodiment 1 or 16, wherein the elevated        temperature comprises a temperature of from 120° C. to 180° C.        29. The method of embodiment 10 or 16, wherein the sufficient        period of time comprises at least 2 hours.        30. The method of embodiment 29, wherein the sufficient period        of time comprises from 2 hours to 18 hours.        31. The method of embodiment 1 or 16, wherein the composition is        adjusted to a pH<7 by adding an acid prior to heating to        elevated temperature.        32. The method of embodiment 31, wherein said acid is selected        from the group consisting of sulfuric acid, hydrochloric acid,        and phosphoric acid.        33. The method of embodiment 31, wherein the pH is adjusted to        from about pH 1 to about pH 6.        34. The method of embodiment 31, wherein the pH is adjusted to        from about pH 2 to about pH 5.        35. The method of embodiment 31, wherein the pH is adjusted to        from about pH 3 to about pH 4.        36. The method of any one of embodiments 1, 10, and 16, wherein        a base is added to said composition prior to the ion exchange        step.        37. A method for obtaining purified succinic acid as a        by-product from a method of making L-glufosinate, said method        comprising:    -   aminating PPO to L-glufosinate by a transaminase (TA) enzyme,        using an amine group from glutamic acid present in the        composition, thereby generating a 2-oxoglutaric acid by-product;    -   reacting an L-glufosinate composition comprising L-glufosinate,        glutamate, and 2-oxoglutaric acid at an elevated temperature for        a sufficient period of time to convert the majority of glutamate        to pyroglutamate;    -   isolating 2-oxoglutaric acid from the composition by size        exclusion chromatography to obtain a composition of        substantially purified 2-oxoglutaric acid; and    -   contacting the substantially purified 2-oxoglutaric acid with        hydrogen peroxide to obtain a composition of substantially        purified succinic acid.        38. The method of embodiment 37, wherein a base is added to said        composition prior to the size exclusion step.        39. The method of embodiment 36 or embodiment 38, wherein said        base is selected from the group consisting of sodium hydroxide,        potassium hydroxide, and ammonium hydroxide.        40. The method of embodiment 36 or embodiment 38, wherein the pH        of said composition is adjusted from about pH 2 to about pH 8.        41. The method of embodiment 36 or embodiment 38, wherein the pH        of said composition is adjusted from about pH 3 to about pH 7.        42. The method of embodiment 36 or embodiment 38, wherein the pH        of said composition is adjusted from about pH 4 to about pH 6.        43. The method of embodiment 36 or embodiment 38, wherein the        resulting composition is processed through a membrane separator.        44. The method of embodiment 36 or embodiment 38, wherein said        composition is cooled to a temperature below about 25° C., held        for a sufficient period of time, and then filtered.        45. The method of embodiment 44, wherein said temperature is no        more than about 20° C.        46. The method of embodiment 44, wherein said temperature is no        more than about 10° C.        47. The method of embodiment 44, wherein said temperature is no        more than about 5° C.        48. The method of embodiment 44, wherein said temperature is no        more than about 0° C.        49. The method of embodiment 44, wherein said sufficient period        of time comprises at least 1 hour.        50. The method of embodiment 49, wherein said sufficient period        of time comprises from 1 hour to 24 hours.        51. The method of any one of embodiments 1, 10, and 16, wherein        said ion exchange is performed by contacting the composition        with either an anion exchange resin or a cation exchange resin.        52. The method of embodiment 51, wherein said ion exchange resin        is comprised of a polymer-based, cross-linked substrate made        from a monovinyl monomer and a polyvinyl crosslinking agent.        53. The method of embodiment 52, wherein said monovinyl monomer        is styrene and the polyvinyl crosslinking agent is        divinylbenzene.        54. The method of embodiment 52, wherein the porosity of said        ion exchange resin is microporous, mesoporous, or macroporous.        55. The method of embodiment 52, wherein the said ion exchange        resin is a gel type resin.        56. The method of embodiment 52, wherein the said ion exchange        resin has a median particle diameter from 10 microns to 2000        microns.        57. The method of embodiment 52, wherein the said ion exchange        resin has a median particle diameter from 100 microns to 1000        microns.        58. The method of embodiment 52, wherein the ion exchange resin        is in the form of a bead with a uniform particle size        distribution.        59. The method of any one or more of embodiments 51 through 58,        wherein the said ion exchange resin is a strong anion exchange        resin.        60. The method of embodiment 59, wherein the said anion exchange        resin is selected from the group consisting of DOWEX™ MARATHON™        A, DOWEX™ MONOSPHERE™ 550A, DOWEX® MONOSPHERE™ MSA, and DOWEX™        XUR-1525-L09-046, an experimental geltype, uniform particle size        in the 300 micron range, strong base anion exchange resin, and        Type I (trimethylamine quaternary ammonium, in the chloride        form).        61. The method of embodiment 59, wherein said anion exchange        resin is used in hydroxy form.        62. The method of any one of embodiments 1, 10, and 16, wherein        said ion exchange process is conducted in a pH range from 3 to        8.        63. The method of any one of embodiments 1, 10, and 16, wherein        said ion exchange process is conducted in a pH range of 4 to 8.        64. The method of any one of embodiments 1, 10, and 16, wherein        said ion exchange process is conducted in a pH range of 5 to 8.        65. The method of any one of embodiments 1, 10, and 16, wherein        said ion exchange process is conducted in a pH range of 6 to 7.        66. The method of any one of embodiments 1, 10, and 16, wherein        the ion exchange process is conducted at a temperature in the        range of from 20° C. to 70° C.        67. The method of any one of embodiments 1, 10, and 16, wherein        the ion exchange process is conducted in a temperature in the        range of from 30° C. to 60° C.        68. The method of any one of embodiments 1, 10, and 16, wherein        the ion exchange process is conducted in a temperature in the        range of from 40° C. to 50° C.        69. The method of any one or more of embodiments 51 through 58,        wherein said ion exchange resin is a strong cation exchange        resin.        70. The method of embodiment 69, wherein said cation exchange        resin is used in a hydrogen form.        71. The method of embodiment 69, wherein said cation exchange        resin is selected from the group consisting of DOWEX™ 50WX8,        DOWEX™ MONOSPHERE™ 99 K/350, DOWEX™ MONOSPHERE™ C, and DOWEX™        MARATHON™ MSC.        72. The method of embodiment 69, wherein said ion exchange        process is conducted in a pH range from 0.4 to 7.        73. The method of embodiment 69, wherein said exchange process        is conducted in a pH range of 0.6 to 7.        74. The method of embodiment 69, wherein the ion exchange        process is conducted in a pH range of 1 to 6.        75. The method of embodiment 69, wherein the ion exchange        process is conducted in a pH range of 1 to 4.5.        76. The method of embodiment 69, wherein the ion exchange        process is conducted at a temperature in the range of from        20° C. to 70° C.        77. The method of embodiment 69, wherein the ion exchange        process is conducted at a temperature in the range of from        30° C. to 60° C.        78. The method of embodiment 69, wherein the ion exchange        process is conducted at a temperature in the range of from        40° C. to 50° C.        79. The method of any one of embodiments 1, 10, and 16, wherein        prior to said ion exchange, the composition is concentrated or        decolorized or both.        80. The method of embodiment 79, wherein the composition is        decolorized with activated charcoal or activated carbon.        81. The method of embodiment 79, wherein the composition is        decolorized with a polymeric material.        82. The method of any one of embodiments 1, 10, and 16, wherein        the composition and ion exchange resin are contacted in batch        mode.        83. The method of any one of embodiments 1, 10, and 16, wherein        the composition and ion exchange resin are contacted in flow        mode.        84. The method of embodiment 83, wherein said flow mode uses the        technique of simulated moving bed chromatography.        85. The method of embodiment 84, wherein the composition is        subjected to a pretreatment adsorption step to remove one or        more components of the composition prior to simulated moving bed        chromatography.        86. A method of regenerating the resin used in the method of any        one of embodiments 1, 10, and 16, wherein the resin is contacted        with a composition comprising one or more of an acid, a base,        water, and an inorganic salt.        87. The method of embodiment 86, wherein the base is sodium        hydroxide.        88. The method of embodiment 86, wherein the inorganic salt is        selected from a group comprised of sodium chloride, sodium        sulfate, ammonium chloride, and ammonium sulfate.        89. The method of embodiment 86, wherein the acid is sulfuric        acid.        90. The method of embodiment 86, wherein the composition        comprises not more than 0.5 M sodium hydroxide and not more than        1.5 M sodium chloride.        91. The method of embodiment 86, wherein the composition        comprises not more than 0.1 M sodium hydroxide and not more than        1.5 M sodium chloride.        92. The method of embodiment 86, wherein the composition        comprises not more than 0.5 M sodium chloride.        93. The method of embodiment 86, wherein the composition        comprises not more than 0.5 M sodium sulfate.        94. The method of embodiment 86, wherein the said regeneration        produces a solution of substantially purified 2-oxoglutaric        acid.        95. The method of embodiment 94, wherein the solution of        substantially purified 2-oxoglutaric acid is contacted with        hydrogen peroxide to produce substantially purified succinic        acid.        96. The method of any one of embodiments 1, 10, and 16, wherein        the substantially purified L-glufosinate is reduced to a        concentrate that can be formulated directly into an herbicidal        product.        97. The method of any one of embodiments 1, 10, and 16, wherein        said substantially purified L-glufosinate is concentrated past        the point where crystallization or precipitation occurs and the        resulting solids are filtered and dried.        98. The method of embodiment 97, wherein a solvent is added        before, during or after said concentration.        99. The method of embodiment 98, wherein the solvent is chosen        from a group comprised of acetone, methanol, ethanol,        1-propanol, 2-propanol, acetonitrile, tetrahydrofuran,        1-methyl-2-propanol, 1,2-propanediol, 1,2-ethanediol,        triethylamine, isopropylamine, and ammonium hydroxide.        100. The method of any one of embodiments 1, 10, and 16, wherein        the substantially purified L-glufosinate is concentrated to        produce a dry solid.        101. The method of any one of embodiments 1, 10, and 16, wherein        the substantially purified L-glufosinate is spray dried.        102. The method of any one of embodiments 1, 10, and 16, wherein        the substantially purified L-glufosinate is partially        concentrated prior to spray drying.        103. The method of any one of embodiments 1, 10, and 16, wherein        formulation ingredients are mixed with the substantially        purified L-glufosinate prior to spray drying.        104. A method for purifying L-glufosinate from a composition        comprising L-glufosinate and glutamate, by converting the        glutamate to pyroglutamate to facilitate isolation of        L-glufosinate, said method comprising:    -   adding sulfuric acid to bring the composition to pH 3.7 to        crystallize glutamate and removing solid glutamate from the        composition;    -   reacting the composition at an elevated temperature for a        sufficient period of time to convert the majority of remaining        glutamate to pyroglutamate;    -   reducing the volume of the composition;    -   adding sodium hydroxide until the pH of the composition is        between pH 6 and pH 7;    -   cooling the composition to a temperature between 5° C. and the        freezing point of the mixture (approximately −10 to −20° C.)        during which sodium sulfate precipitates;    -   filtering the sodium sulfate crystals from the composition;    -   contacting the composition with an ion exchange resin to remove        pyroglutamic acid and obtaining a composition of substantially        purified L-glufosinate; and,    -   reducing the volume of the composition of the substantially        purified L-glufosinate.        105. The method of embodiment 104, wherein the volume of the        composition of the substantially purified L-glufosinate is        reduced to a solid.        106. The method of embodiment 104, wherein the volume of the        composition of the substantially purified L-glufosinate is        concentrated to an amount suitable for use in an herbicidal        formula.        107. The method of embodiment 104, wherein said solid glutamate        is removed by filtration or centrifugation from the composition.        108. The method of embodiment 104, wherein the volume of the        composition is reduced by vacuum distillation, membrane        separation, evaporation thin film evaporation, or wiped film        evaporation.        109. The method of embodiment 104, wherein said sodium sulfate        crystals are filtered from the composition by filtration or        centrifugation.        110. L-Glufosinate ammonium Form A, which is characterized by an        X-ray powder diffraction (XRPD) pattern comprises at least three        peaks selected from 10.1, 10.8, 16.8, 17.2, 18.3, 20.0, 20.2,        21.2, 21.5, 24.1, 24.3, 25.1, 25.6, 26.9, 28.6, 29.0, 29.7,        29.9, 31.9, 33.4, 33.7, 34.5, 34.9, 35.4, 35.7, 36.1, 36.7,        37.1, 37.5, 38.2, and 39.8° 2θ, ±0.2° 2θ, as determined on a        diffractometer using Cu-Kα radiation.        111. L-Glufosinate ammonium Form A according to embodiment 110,        wherein the XRPD pattern comprises at least six peaks selected        from 10.1, 16.8, 18.3, 21.2, 24.1, 24.3, 25.6, 26.9, 28.6, 29.0,        and 34.5° 2θ, ±0.2° 2θ.        112. L-Glufosinate ammonium Form A according to embodiment 110,        wherein the XRPD pattern comprises at least ten peaks selected        from 10.1, 16.8, 18.3, 21.2, 24.1, 24.3, 25.6, 26.9, 28.6, 29.0,        and 34.5° 2θ, ±0.2° 2θ.        113. L-Glufosinate ammonium Form A according to embodiment 110,        wherein the XRPD pattern is substantially in accordance with        FIG. 1 .        114. L-Glufosinate Form B, which is characterized by an X-ray        powder diffraction (XRPD) pattern comprises at least three peaks        selected from 10.0, 11.4, 12.5, 16.5, 17.4, 18.1, 19.6, 20.0,        21.8, 22.9, 23.6, 24.0, 25.1, 25.5, 26.1, 26.3, 26.4, 27.9,        28.2, 28.4, 28.7, 29.2, 30.2, 30.9, 31.6, 31.7, 32.7, 33.0,        33.3, 34.3, 35.2, 36.7, 37.2, 37.4, 37.8, 38.3, 38.7, and 39.3°        2θ, ±0.2° 2θ, as determined on a diffractometer using Cu-Kα        radiation.        115. L-Glufosinate Form B according to embodiment 114, wherein        the XRPD pattern comprises at least six peaks selected from        10.0, 12.5, 16.5, 17.4, 18.1, 19.6, 20.0, 21.8, 22.9, 23.6,        24.0, 25.5, 26.3, 26.4, 29.2, 34.3, 35.2, and 37.4° 2θ, ±0.2°        2θ.        116. L-Glufosinate Form B according to embodiment 114, wherein        the XRPD pattern comprises at least ten peaks selected from        10.0, 12.5, 16.5, 17.4, 18.1, 19.6, 20.0, 21.8, 22.9, 23.6,        24.0, 25.5, 26.3, 26.4, 29.2, 34.3, 35.2, and 37.4° 2θ, ±0.2°        2θ.        117. L-Glufosinate Form B according to embodiment 114, wherein        the XRPD pattern is substantially in accordance with FIG. 3 .        118. L-Glufosinate ammonium Form C, which is characterized by an        X-ray powder diffraction (XRPD) pattern comprises at least three        peaks selected from 9.1, 10.9, 16.1, 16.8, 17.3, 18.3, 20.1,        21.4, 21.8, 22.4, 22.7, 24.1, 24.9, 25.4, 25.6, 26.1, 26.6,        27.7, 28.3, 28.9, 30.8, 31.9, 32.6, 33.6, 33.9, 35.1, 36.6,        37.1, 37.5, 38.3, 38.9, and 39.7° 2θ, ±0.2° 2θ, as determined on        a diffractometer using Cu-Kα radiation.        119. L-Glufosinate ammonium Form C according to embodiment 118,        wherein the XRPD pattern comprises at least six peaks selected        from 9.1, 16.1, 16.8, 17.3, 21.8, 24.1, 24.9, 25.6, 26.1, 28.3,        and 28.9° 2θ, ±0.2° 2θ.        120. L-Glufosinate ammonium Form C according to embodiment 118,        wherein the XRPD pattern comprises at least ten peaks selected        from 9.1, 16.1, 16.8, 17.3, 21.8, 24.1, 24.9, 25.6, 26.1, 28.3,        and 28.9° 2θ, ±0.2° 2θ.        121. L-Glufosinate ammonium Form C according to embodiment 118,        wherein the XRPD pattern is substantially in accordance with        FIG. 5 .        122. L-Glufosinate Form D, which is characterized by an X-ray        powder diffraction (XRPD) pattern comprises at least three peaks        selected from 9.1, 11.6, 13.1, 14.1, 14.4, 16.2, 17.7, 18.2,        18.9, 19.3, 19.7, 21.2, 21.8, 22.4, 23.2, 23.5, 25.3, 25.8,        26.2, 27.2, 28.6, 29.1, 30.0, 30.6, 31.1, 31.6, 32.7, 33.5,        34.4, 34.7, 35.4, 35.9, 36.4, and 37.4° 2θ, ±0.2° 2θ, as        determined on a diffractometer using Cu-Kα radiation.        123. L-Glufosinate Form D according to embodiment 122, wherein        the XRPD pattern comprises at least six peaks selected from 9.1,        17.7, 18.2, 18.9, 22.4, 23.2, 23.5, 26.2, 33.5, and 36.4° 2θ,        ±0.2° 2θ.        124. L-Glufosinate Form D according to embodiment 122, wherein        the XRPD pattern comprises peaks at 9.1, 17.7, 18.2, 18.9, 22.4,        23.2, 23.5, 26.2, 33.5, and 36.4° 2θ, ±0.2° 2θ.        125. L-Glufosinate Form D according to embodiment 122, wherein        the XRPD pattern is substantially in accordance with FIG. 7 .        126. L-Glufosinate hydrochloride Form E, which is characterized        by an X-ray powder diffraction (XRPD) pattern comprises at least        three peaks selected from 13.1, 16.8, 18.2, 19.4, 20.5, 20.9,        21.4, 22.5, 23.4, 25.3, 26.2, 26.5, 26.9, 27.8, 28.1, 30.2,        31.2, 31.5, 32.3, 33.8, 34.4, 35.3, 35.7, 36.3, 36.9, 37.8,        38.2, 38.8, and 39.4° 2θ, ±0.2° 2θ, as determined on a        diffractometer using Cu-Kα radiation.        127. L-Glufosinate hydrochloride Form E according to embodiment        126, wherein the XRPD pattern comprises at least six peaks        selected from 16.8, 18.2, 20.5, 21.4, 22.5, 22.9, 23.4, 25.3,        30.2, and 31.2° 2θ, ±0.2° 2θ.        128. L-Glufosinate hydrochloride Form E according to embodiment        126, wherein the XRPD pattern comprises at least ten peaks        selected from 16.8, 18.2, 20.5, 21.4, 22.5, 22.9, 23.4, 25.3,        30.2, and 31.2° 2θ, ±0.2° 2θ.        129. L-Glufosinate hydrochloride Form E according to embodiment        126, wherein the XRPD pattern is substantially in accordance        with FIG. 9 .        130. Solid L-glufosinate ammonium, which is X-ray amorphous.

The following examples are offered by way of illustration and not by wayof limitation.

EXAMPLES Example 1: De-Racemization of Racemic D/L-Glufosinate at a 3 LReaction Size

In this example, the reaction was run in a 3 L stirred, jacketedreactor. The following reagents were added at the start of the reaction:900 mM D,L-glufosinate, 2700 mM glutamate, and 2,535 grams of water.After heating to 30° C., the pH was adjusted to 7.8 using approximately45 grams of 3N NaOH. To the reactor was added 0.30 grams of antifoamAF204 (Sigma-Aldrich) and 0.60 grams of catalase dissolved in 10 mL ofwater. To the reactor were charged 188 grams of plastic beads on whichwere immobilized 6 g AC302 DAAO, and 0.9 g E. coli gab T transaminasefollowed by 400 grams of water. During the course of the stirredreaction, oxygen-enriched air (35% 02, 65% N2) was introduced at 1.7 VVM(volumes of gas per volume of reaction mixture per minute) via twostainless steel sparging stones. HPLC analysis of the reactiondemonstrated that equilibrium was reached within 10 hours, with theenantiomeric excess of L-glufosinate over D-glufosinate greater than 99%and the ratio of L-glufosinate to PPO 90% to 10%. This result indicatesan efficient deracemization of D/L-glufosinate into L-glufosinate by theRgDAAO/EcgabT enzyme couple at the larger scale.

Example 2: Crystallization of Glutamic Acid Using ConcentratedHydrochloric Acid

Following a procedure similar to Example 1, beads were removed byfiltration and the filtrate was heated to 35° C. Concentratedhydrochloric acid was slowly added to the batch until the pH reached3.7. The batch was heated to 60° C. in a heating bath and held for 60minutes. The heating bath was switched off and the batch was allowed tocool to ambient temperature overnight. The batch was cooled to 0° C. andheld for one hour. The white precipitate was removed by filtration. Themolar ratio of L-glufosinate to glutamic acid in the filtrate wasdetermined by NMR analysis to be 88:12.

Example 3: Crystallization of Glutamic Acid Using Concentrated SulfuricAcid

Following a procedure similar to Example 1, beads were removed byfiltration and the filtrate was heated to 35° C. Concentrated sulfuricacid was slowly added to the batch until the pH reached 3.7. The batchwas heated to 60° C. in a heating bath and held for 60 minutes. Theheating bath was switched off and the batch was allowed to cool toambient temperature overnight. The batch was cooled to 0° C. and heldfor one hour. The white precipitate was removed by filtration. The molarratio of L-glufosinate to glutamic acid in the filtrate was determinedby NMR analysis to be 85:15.

Example 4: Formation of Pyroglutamic Acid

Following a procedure similar to Example 2, a portion of the filtratewas heated to 140° C. for 3.5 hours in an autoclave. NMR analysis of asample of the reaction mass showed a 95:5 molar ratio of L-glufosinateto glutamic acid. NMR analysis also confirmed the presence ofpyroglutamic acid. No evidence of L-glufosinate decomposition wasobserved in the NMR result.

Example 5: Formation of Pyroglutamic Acid

Following a procedure similar to Example 3, a portion of the filtratewas further adjusted to pH 3.0 using sulfuric acid. The concentration ofL-glufosinate was approximately 310 mM prior to pH adjustment. Theliquid was then heated to 125° C. for 18 hours in an autoclave. NMRanalysis of a sample of the reaction mass showed a 98:2 molar ratio ofL-glufosinate to glutamic acid. NMR analysis also confirmed the presenceof pyroglutamic acid. No evidence of L-glufosinate decomposition wasobserved in the NMR result.

Example 6: Concentration of Reaction Mass Followed by Formation ofPyroglutamic Acid

Following a procedure similar to Example 3, the filtrate wasconcentrated by vacuum distillation to a concentration of L-glufosinateof approximately 412 mM. A portion of the concentrated solution wasfurther adjusted to pH 3.0 using sulfuric acid. The liquid was thenheated to 125° C. for 18 hours in an autoclave. NMR analysis of a sampleof the reaction mass showed a 98:2 molar ratio of L-glufosinate toglutamic acid. NMR analysis also confirmed the presence of pyroglutamicacid. No evidence of L-glufosinate decomposition was observed in the NMRresult.

Example 7: Concentration of Reaction Mass Followed by Cooling andPrecipitation of Sodium Sulfate

Following a procedure similar to Example 5, the reaction mass after thecyclization reaction was concentrated by vacuum distillation to aconcentration of L-glufosinate of approximately 404 mM and then cooledto room temperature. A 300 mL portion of the concentrated solution wastransferred to a beaker and the pH was adjusted to 6.2 by adding 11.7grams of solid sodium hydroxide (97%, Sigma-Aldrich). The beaker wasplaced in a freezer at −20° C. for about 4 hours during which the entiremixture froze. The beaker was removed from the freezer and placed in anice bath at approximately 0° C. for about four hours. Periodicallyduring this time, the contents were gently mixed by hand. The contentsof the beaker were filtered on filter paper using a Büchner funnelprecooled to about 4° C. The weight of the filtrate was 247 grams andthe volume of the filtrate was 215 mL. The concentration ofL-glufosinate was approximately 550 mM. The total weight of the crystalsafter all the liquid had drained was 115 grams; HPLC analysis of thecrystals indicated only a trace amount of L-glufosinate and otherorganic impurities. A 10-gram portion of the dry crystals wastransferred to a beaker which was placed in an incubator heated to 45°C. Shortly afterward, it was observed that almost all of the crystalshad melted. The melting point of sodium sulfate decahydrate is 32.38° C.according to the Handbook of Chemistry and Physics (63^(rd) Ed. (1982),R. C. Weast, Ed.; CRC Press, Inc., Boca Raton, Fla.; page B-150). Thebeaker was removed from the incubator and placed in a water bath. Thewater bath was brought to boil. Eventually, the liquid in the beakerdisappeared, leaving behind a solid. After all of the liquid had beenremoved from the beaker by evaporation, the beaker was cooled and theremaining solid was weighed. Approximately 4.2 grams of solid remainedin the beaker.

Example 8: Formation of Pyroglutamic Acid and Purification with CationExchange Resin (Batch Mode)

Following a procedure similar to Example 1, beads were removed byfiltration and concentrated HCl was slowly added to the batch until thepH reached 4.0. The white precipitate was removed by filtration. Aportion of the filtrate was then heated to 140° C. for 4 hours in anautoclave. NMR analysis of a sample of the reaction mass showed >94%conversion of glutamic acid to pyroglutamic acid.

After cooling to room temperature, 37% HCl was added to adjust thesolution to pH 1. The solution was treated with prewashed DOWEX™ 50WX8cation exchange resin. In the treatment, the solution was allowed to mixwith the resin for 30 minutes after which the resin was isolated on afilter. The resin was then washed with water and then eluted with 4MNH₄OH. The eluent was concentrated under vacuum to a solid containing90-98% pure L-glufosinate and 2-10% glutamic acid both as theirmono-ammonium salts as determined by NMR.

Example 9: Purification Using an Anion Exchange Resin in a Column (FlowMode)

A jacketed glass column, 1″ diameter and 24″ length, was packed with astrong base anion exchange resin (DOWEX™ XUR-1525-L09-046, anexperimental, gel-type, uniform particle size in the range of 300microns, strong base anion resin, Type I (trimethylamine quaternaryammonium, in the chloride form, obtained from the Dow Chemical Company))which had been converted to the hydroxy form. The column of resin washeated to about 60° C. and flushed with water until the pH of theeffluent was approximately pH 6. To the column was pumped 270 mL of asolution prepared following a procedure similar to Example 5; prior topumping, the solution was adjusted to pH 6 with NaOH and heated to about60° C. The flow rate was approximately 10.5 mL/min. When the feed of thereaction mixture to the column was complete, approximately 900 mL ofwater adjusted to pH 6 was fed to the column. Approximately 100 mL ofcolumn effluent was collected and discarded as void volume after which65 fractions of approximately 12 mL each were collected using a fractioncollector. The fractions were analyzed by HPLC/UV and Table 1 belowshows the concentrations of L-glufosinate and the other components.

TABLE 1 L-glufosinate Pyroglutamic acid 2-oxoglutarate PPO Fraction #(mM) (mM) (mM) (mM) 1 0 0.045 0 0 4 0 0.044 0 0 7 10.3 0.11 1.5 0 10 1040.89 3.1 0 13 138 1.06 2.8 0 16 165 0.93 2.3 0 19 171 2.57 2.7 0 22 18217.2 3.5 0 25 157 51.4 0.77 0 7-22 130 2.08 2.6 0

The last row in Table 1 shows the HPLC result after fractions 7 through22 were combined into a single solution of substantially purifiedL-glufosinate.

Example 10: Purification of Concentrated Reaction Mass Using an AnionExchange Resin in a Column (Flow Mode)

A solution was prepared following a procedure similar to Example 5,except the solution was concentrated by vacuum distillation. The volumeof the solution was reduced by a factor of approximately 2.3. Thesolution was adjusted to pH 6.7 using NaOH and heated to approximately60° C. Following a procedure similar to Example 8, 270 mL of thesolution was fed to a strong base anion resin (DOWEX™ XUR-1525-L09-046,an experimental, gel-type, uniform particle size in the range of 300microns, strong base anion resin, Type I (trimethylamine quaternaryammonium, in the chloride form, obtained from the Dow Chemical Company))which had been converted to the hydroxy form. Prior to feeding thesolution, the column of resin was heated to about 60° C. and flushedwith water until the pH of the effluent was approximately pH 6. The flowrate was approximately 10.5 mL/min. When the feed of the reactionmixture to the column was complete, approximately 900 mL water adjustedto pH 6 was fed to the column. Approximately 100 mL of column effluentwas collected and discarded as void volume after which 66 fractions ofapproximately 15 mL each were collected using a fraction collector. Thefractions were analyzed by HPLC/UV and Table 2 below shows theconcentrations of L-glufosinate and other components.

TABLE 2 L-glufosinate Pyroglutamic acid 2-oxoglutarate PPO Fraction #(mM) (mM) (mM) (mM) 1 0 0.20 0 0 4 0 0.38 0 0 7 148 2.5 0 0 10 281 0 0 013 320 2.5 0 0 16 335 10 3.7 0 19 310 86 8.9 0 22 299 218 14 0 25 1799.7 0 0 6-19 385 15.7 3.6 0The last row in Table 2 shows the HPLC result after fractions 6 through19 were combined into a single solution of substantially purifiedL-glufosinate.

Example 11: Purification of Concentrated Reaction Mass Using an AnionExchange Resin in a Column at 35° C. (Flow Mode)

A solution was prepared following a procedure similar to Example 5. Thesolution was adjusted to pH 6.2 using NaOH and heated to approximately35° C. Following a procedure similar to Example 8, 270 mL of thesolution was fed to a strong base anion resin (DOWEX™ MONOSPHERE™ 550Ain hydroxide form, a product of the Dow Chemical Company). Prior tofeeding the solution, the column of resin was heated to about 35° C. andflushed with water until the pH of the effluent was approximately pH 7.The flow rate was approximately 5.5 mL/min. When the feed of thereaction mixture to the column was complete, approximately 1000 mL ofwater adjusted to pH 7 was fed to the column. Approximately 100 mL ofcolumn effluent was collected and discarded as void volume after which44 fractions of approximately 15 mL each were collected using a fractioncollector. The fractions were analyzed by HPLC/UV and Table 3 belowshows the concentrations of L-glufosinate and other components.

TABLE 3 L-glufosinate Pyroglutamic acid 2-oxoglutarate PPO Fraction #(mM) (mM) (mM) (mM) 1 0 0 0 0 3 0 0 0 0 5 48 0 0 0 7 319 2.5 0 0 9 1873.5 0.54 0 11 135 4.6 1.2 0 13 116 8.9 1.3 0 15 155 24 2.1 0 17 169 47 00 19 152 64 0 0 21 141 80 0 0 23 62 103 0 0 25 0 7.9 0 0 5-15 113 5.70.6 0The last row in Table 3 shows the HPLC result after fractions 5 through15 were combined into a single solution of substantially purifiedL-glufosinate.

Example 12: Purification of the Reaction Mass Using an Anion ExchangeResin in Two Columns Operated in Series at 25° C. (Flow Mode)

Two 24″ columns were packed with a strong base anion resin (DOWEX™XUR-1525-L09-046, an experimental, gel-type, uniform particle size inthe range of 300 microns, strong base anion resin, Type I(trimethylamine quaternary ammonium, in the chloride form, obtained fromthe Dow Chemical Company)) which had been converted to the hydroxy form.The columns were maintained at a temperature of about 25° C. Tubing andmulti-port valves were connected to the inlet of each column so thatreaction mixture, pH 6 water, or resin regeneration solution could beadded individually. Tubing and multi-port valves were connected to theoutlet of the first column so that fluid exiting the first column couldeither be collected by a fraction collector or transferred to the inletof the second column. Both columns were flushed with water at about pH 6until the pH of the effluent was approximately pH 6. A reaction mixturewas prepared following a procedure similar to Example 5 and adjusted toabout pH 6.4. About 270 mL of the reaction mixture was pumped to thefirst column at a flow rate of approximately 10.5 mL/min. Following thefeed of the reaction mixture, about 210 mL of pH 6 water was fed to thecolumn; therefore, the total volume fed to the first column was 480 mL.A total of 330 mL of fluid exiting the first column was collected infractions of about 15 mL each. After the last fraction was collected,the valves were set to pump the next 150 mL exiting the first column tothe inlet of the second column. Following the feed from the first columnto the second column, about 270 mL of the reaction mixture was fed tothe inlet of the second column after which 600 mL of pH 6 water was fed.Therefore, a total volume of 1020 mL was fed to the second column. Allof the fluid exiting the second column was collected in fractions ofabout 15 mL. Fractions collected from both columns were analyzed byHPLC. Table 4 below shows fractions collected from the first column.

TABLE 4 L-glufosinate Pyroglutamic acid 2-oxoglutarate PPO Fraction #(mM) (mM) (mM) (mM) 1 0 0 0 0 4 0 0 0 0 5 30 0 0 0 6 70 0 0 0 7 111 0 00 10 156 1.1 0 0 13 178 12 0 0 16 186 50 1.0 0 7-15 146 6.4 0.7 0The last row in Table 4 shows the HPLC result after fractions 7 through15 were combined into a single solution of substantially purifiedL-glufosinate.

Table 5 below shows fractions collected from the second column.

TABLE 5 L-glufosinate Pyroglutamic acid 2-oxoglutarate PPO Fraction #(mM) (mM) (mM) (mM) 1 0 0 0 0 4 0 0 0 0 7 0 0 0 0 10 0 0.54 0 0 13 85 00 0 16 159 0 0 0 19 89 4.9 0 0 22 159 24 0 0 25 166 55 0 0 28 177 86 0 031 174 111 0 0 34 184 135 0 0 37 181 560 4.0 0 40 0 3.1 0 0 12-22 1314.5 0.7 0The last row in Table 5 shows the HPLC result after fractions 12 through22 were combined into a single solution of substantially purifiedL-glufosinate.

Example 13: Production of Purified 2-Oxoglutaric Acid Obtained afterAnion Exchange Purification and Resin Regeneration

Following a procedure similar to Example 8, after the feed of wateradjusted to pH 6 to the column was complete, a solution of 0.1 M sodiumhydroxide and 1.5 sodium chloride was fed to the column at about 60° C.and approximately 10.5 mL/min; 88 fractions of 15 mL each werecollected. Analysis of the fractions by HPLC showed that 2-oxoglutaricacid eluted over a very narrow range of fractions as shown in Table 6below.

TABLE 6 L-glufosinate Pyroglutamic 2-oxoglutarate PPO Fraction # (mM)acid (mM) (mM) (mM) 1 0 0.14 0 0 11 0 0.89 1.2 0 22 0 1.2 3.0 0 27 00.69 113 0 28 0 0 325 0 30 0 0 66 0 33 0 0 2.7 0 44 0 0.47 0 02-Oxoglutarate was not detected in fraction 44 or any other fractioncollected after fraction 44 and selected for analysis. The amount of2-oxoglutarate in this experiment exceeds the amount expected from asingle ion exchange experiment. Not to be bound by theory, it is likelythat the resin was not sufficiently regenerated prior to thisexperiment.

Example 14: Production of Succinic Acid from 2-Oxoglutaric Acid Obtainedafter Anion Exchange Purification and Resin Regeneration

Following a procedure similar to Example 12, a fraction containing 180mM 2-oxoglutarate was produced. A 0.266 mL sample of this fraction wascombined with 1.5 molar equivalents of hydrogen peroxide (0.128 M) anddiluted to a total volume of 0.5 mL in a container. The container wasshaken at 30° C. and sampled approximately every 5 minutes for HPLCanalysis. After 10 minutes, approximately 70% of the 2-oxoglutamic acidhad been converted to succinic acid.

Example 15: Decolorization of Reaction Mixture Obtained after ConvertingGlutamic Acid to Pyroglutamic Acid

Various amounts of activated carbon (0.25 wt. %, 0.5 wt. %, 1.0 wt. %,3.0 wt. %, and 5.0 wt. %) were added to portions of a reaction mixtureresulting from the conversion of glutamic acid to pyroglutamic acid, asdescribed above. After mixing for approximately 20 minutes at roomtemperature, the activated carbon was filtered on top of a bed ofpre-washed Celite®. The resulting filter cake was then washed with waterand the cake was combined with the filtrate. The filtrate was thenchecked for L-glufosinate recovery relative to an untreated sample usingpyroglutamic acid as an internal standard. Table 7 below shows therecovery and color observations.

TABLE 7 Activated carbon L-glufosinate recovery (wt. %) (%) Colorobservation 0.25 104 Slightly orange 0.5 103 Slightly orange 1.0 98Slightly orange 3.0 103 No color 5.0 98 No color

Example 16: Preparation and Characterization of L-Glufosinate Polymorphs

Two lots of L-glufosinate ammonium were received and used in the studiesdescribed below. XRPD analysis of one of the lots confirmed the sampleto be x-ray amorphous. IC analysis of another lot showed the ammoniumcontent of the sample to be substoichiometric.

Solubility levels of L-glufosinate ammonium were determined, showingthat the material was very soluble in water and poorly soluble in mostorganic solvents. Organic/aqueous mixtures were prone to oil formation.Organic solubility generally remained poor in solvents such as dimethylsulfoxide, dimethyl acetamide, and N-methyl-2-pyrrolidone.Trifluoroethanol (TFE) was the only organic solvent to show solubilityof >2 mg/mL.

The polymorph screen of L-glufosinate ammonium was conducted usingdifferent crystallization techniques to vary conditions of nucleationand growth investigating both thermodynamic and kinetic conditions.Crystallization techniques included slurrying at room temperature andelevated temperature, evaporation, antisolvent addition/precipitation,and cooling. Kinetic factors such as cooling rate, evaporation rate, orantisolvent addition rate were varied during these experiments.Non-solvent based techniques such as vapor stress and heating of theL-glufosinate ammonium amorphous material above the glass transitiontemperature were also utilized.

An attempt was made to vary the solvent systems utilized during thepolymorph screen however due to the limited solubility in most organicsolvent systems, in many cases water or TFE were added to improve thesolubility. Experiments in neat solvents generally consisted of longterm slurries at room temperature or elevated temperature. The formationof hydrates was also investigated through crystallization experimentsconducted in water and aqueous-organic systems with varying wateractivities, however gels and oils were observed in many of these solventsystems. Anhydrous conditions were also investigated to determine if newforms could be generated under these conditions. In these experiments,the L-glufosinate ammonium starting material was pre-dried overdesiccant to remove any potential residual moisture from the startingmaterial.

Selected crystallization experiments were conducted utilizing excessammonium hydroxide due to the sub-stoichiometric amount of ammoniumobserved in some of the starting materials. Similarly, a few experimentswere conducted under acidic conditions with HCl.

Five unique crystalline L-glufosinate materials were observed during thescreen and were designated as Form A, Form B, Form C, Form D, and FormE. Form A and Form C appear to be metastable forms of L-glufosinateammonium that are prone to conversion to Form B. Form B and Form Dappear to be anhydrous crystalline forms of the L-glufosinate free form.Form E is an apparent L-glufosinate HCl salt.

Crash Cooling (CC): Solutions of L-glufosinate ammonium were prepared inselected solvents or solvent mixtures at elevated temperature. Once theclear solution was obtained after visual observation, the solution wasfiltered through a 0.2 μm or 0.45 μm syringe filter into a preheatedvial. The vial was then capped and immediately placed in a pre-cooledreactor at sub-ambient temperature. The solids were collected bycentrifugal or vacuum filtration and analyzed.

Conversion Slurry: Form B with additional peaks was slurried inethanol/water (95/5 v/v) at ambient temperature for one day. Seeds ofBIPXAZ (Cambridge Structural Database, Version 5.38, November 2016) withadditional peaks and Form D were added and the mixture was slurried foran extended period at ambient temperature. The solids were collected bycentrifugal filtration and then analyzed.

Fast Cooling (FC): Solutions of L-glufosinate ammonium were prepared inselected solvents or solvent mixtures at elevated temperature. Once theclear solution was obtained after visual observation, the solution wasfiltered through a 0.2 μm or 0.45 μm syringe filter into a preheatedvial. The vial was then capped and immediately placed at ambienttemperature. The solids were collected by centrifugal or vacuumfiltration and analyzed.

Fast Evaporation (FE): Solutions of L-glufosinate ammonium were preparedin selected solvents or solvent mixtures at ambient temperature. Oncethe clear solution was obtained after visual observation, the solutionwas filtered through a 0.2 μm or 0.45 μm syringe filter into a cleanvial. The solution was then allowed to evaporate under ambienttemperatures. The solids were collected in a closed vial and thenanalyzed.

Rotary Evaporation: Solutions of L-glufosinate ammonium were prepared invarious solvents at ambient temperature. The solution was filtered intoa clean vial and solvent-stripped using a rotary evaporator. The solidswere collected in a closed vial and then analyzed.

Slow Cooling: Solutions of L-glufosinate ammonium were prepared indifferent solvents or solvent mixtures at elevated temperature in ametal block. Once the clear solution was obtained after visualobservation, the solution was filtered through a 0.2 μm or 0.45 μmsyringe filter in a preheated vial. The solution was then allowed tocool slowly to ambient temperature. The solids were collected bycentrifugal or vacuum filtration and then analyzed.

Slurry: Slurries of L-glufosinate ammonium were prepared by addingsufficient solids to a given solvent or solvent mixture at ambient orelevated temperature such that undissolved solids were present. Themixture was then stirred in a closed vial at ambient, sub-ambient orelevated temperature for an extended period of time. The solids werecollected by centrifugal or vacuum filtration and then analyzed.

Vapor Stress (VS): Solids of L-glufosinate ammonium was transferred to a1-dram vial, which was then placed inside a 20-mL vial containingsolvent. The 1-dram vial was left uncapped and the 20-mL vial was cappedto allow vapor stressing to occur. Vapor stressing experiments wereconducted at ambient and temperatures. Solids were isolated bydecantation and analyzed.

Vapor Diffusion (VD): Concentrated solutions of L-glufosinate ammoniumwere prepared in different solvents or solvent mixtures at ambienttemperature in a metal block. Once the clear solution was obtained aftervisual observation, the solution was filtered through a 0.2 μm or 0.45μm nylon syringe filter in a clean vial. This vial was placed uncappedin a larger vial containing an antisolvent. The larger vial was cappedto allow vapor diffusion to occur. Solids were isolated by decantation,collected in a closed vial and then analyzed.

Differential Scanning calorimetry (DSC): DSC was performed using aMettler Toledo TGA/DSC 3+. Temperature calibration was performed usingNIST-traceable indium metal. Temperature calibration was performed usingadamantane, phenyl salicylate, indium, tin, and zinc. The sample wasplaced into an aluminum DSC pan, covered with a lid, and the weight wasaccurately recorded. A weighed aluminum pan configured as the sample panwas placed on the reference side of the cell. The pan lid was piercedprior to sample analysis. Data were obtained using a heating rate of 10°C./min over the range of ambient temperature to 350° C. or cycled fromambient temperature to −30° C. to 250° C.

Modulated DSC data were obtained on a TA Instruments Q2000 differentialscanning calorimeter equipped with a refrigerated cooling system (RCS).Temperature calibration was performed using NIST-traceable indium metal.The sample was placed into an aluminum DSC pan, and the weight wasaccurately recorded. The pan was covered with a lid perforated with alaser pinhole, and the lid was crimped. A weighed, crimped aluminum panwas placed on the reference side of the cell. Data were obtained using amodulation amplitude of ±0.08° C. and a 60 second period with anunderlying heating rate of 2° C./minute from ambient temperature to 300°C. The reported glass transition temperatures are obtained from theinflection point of the step change in the reversing heat flow versustemperature curve.

Thermogravimetric (TG) Analysis: TG analysis was performed using aMettler Toledo TGA/DSC3+ analyzer or a TA Instruments Q5000 IRthermogravimetric analyzer. Q5000IR. Temperature calibration wasperformed using phenyl salicylate, indium, tin, and zinc. The sample wasplaced in an aluminum pan. The sample was sealed, the lid pierced, theninserted into the TG furnace. The furnace was heated under nitrogen.Data were obtained using a heating rate of 10° C./min over the range ofambient temperature to 350° C.

Nuclear Magnetic Resonance (NMR) Spectroscopy: The solution NMR spectrumwas acquired with an Agilent DD2-400 spectrometer at SSCI. The samplewas prepared by dissolving a small amount of sample in D₂O/TSP-d2.Additional data were acquired at Spectral Data Services, Inc.,Champaign, Ill. in D₂O/TSP-d2 or CF₃CD₂OD. The data acquisitionparameters are displayed in the first each plot of the spectrum in theData section of this report.

Polarized Light Microscopy (PLM): Polarized light microscopy wasperformed using an optical microscope with crossed polarizers or astereomicroscope with first order red compensator.

X-ray Power Diffraction (XRPD), Reflection Mode: XRPD patterns werecollected with a PANalytical X′Pert PRO MPD diffractometer using anincident beam of Cu Kα radiation produced using a long, fine-focussource and a nickel filter. The diffractometer was configured using thesymmetric Bragg-Brentano geometry. Prior to the analysis, a siliconspecimen (NIST SRM 640e) was analyzed to verify the observed position ofthe Si 111 peak is consistent with the NIST-certified position. Aspecimen of the sample was prepared as a thin, circular layer centeredon a silicon zero-background substrate. Antiscatter slits (SS) were usedto minimize the background generated by air. Soller slits for theincident and diffracted beams were used to minimize broadening fromaxial divergence. Diffraction patterns were collected using a scanningposition-sensitive detector (X′Celerator) located 240 mm from the sampleand Data Collector software v. 2.2b.

XRPD, Transmission Mode: XRPD patterns were collected with a PANalyticalX′Pert PRO MPD diffractometer using an incident beam of Cu radiationproduced using an Optix long, fine-focus source. An elliptically gradedmultilayer mirror was used to focus Cu Kα X-rays through the specimenand onto the detector. Prior to the analysis, a silicon specimen (NISTSRM 640e) was analyzed to verify the observed position of the Si 111peak is consistent with the NIST-certified position. A specimen of thesample was sandwiched between 3-μm-thick films and analyzed intransmission geometry. A beam-stop, short antiscatter extension,antiscatter knife edge were used to minimize the background generated byair. Soller slits for the incident and diffracted beams were used tominimize broadening from axial divergence. Diffraction patterns werecollected using a scanning position-sensitive detector (X′Celerator)located 240 mm from the specimen and Data Collector software v. 2.2b.

1. Form A

L-Glufosinate ammonium Form A was first prepared from an IPA slurry ofmaterial that had been stripped from an aqueous solution. Form A was themost frequently observed material prepared during the study, although itwas frequently observed as a mixture with Form D, Form C, or x-rayamorphous material. Form A was generated from several long term slurriesat elevated temperature or room temperature.

In one instance, Form A was isolated from a seven day slurry in 93/7 v/vmethanol/water. The XRPD pattern for the sample indicated that thesample was composed primarily of a single crystalline phase (FIG. 1 ). Aminor additional peak was observed at a diffraction angle of ˜19.0°. The¹H NMR spectrum of the material was consistent with L-glufosinate andcontained chemical shifts consistent with methanol. Ion chromatographyanalysis indicated 6.4 wt % ammonium content which is less than would beexpected for a theoretical mono ammonium salt (9.1 wt %) and slightlyless than the as-received material (7.0 wt %). Thermal analysis of thematerial was consistent with an anhydrous/non-solvated form. Nosignificant events were observed in the DSC prior to a large endothermat ˜123° C. (onset). A significant change in the slope of the TGA wasobserved around this temperature suggesting a potentialmelt/decomposition event. It was noted that the thermal behavior of thissample was very similar to L-glufosinate Form B. The sample wasreanalyzed by XRPD and it was found that Form A had converted to Form Bwith minor additional peaks upon storage over desiccant. The resultssuggest that Form A is metastable and prone to conversion.

A new sample of Form A was prepared by slurrying as-receivedL-glufosinate ammonium in methanol with ˜1 molar excess of ammoniumhydroxide. Thermal analysis of this sample (FIG. 2 ) however wasconsistent with the previous analysis showing minor weight loss prior toa significant weight loss beginning at ˜116° C. likely due to the onsetof decomposition of the material. A single endotherm was observed withan onset of ˜119° C. The data is suggestive of a melt/decompositionevent.

2. Form B

Form B of L-glufosinate was initially observed from a multistepcrystallization involving slurrying L-glufosinate ammonium in IPA/waterto form a gel and reslurry of the gel in acetone at room temperature.Form B was recovered from several slurries typically involvingorganic-water mixtures at higher water activities. The XRPD pattern ofForm B was successfully indexed (FIG. 3 ) however several minoradditional peaks were observed in the pattern. In fact, Form B wastypically observed with minor additional peaks.

Form B was characterized by ¹H NMR, IC, DSC, and TGA. The ¹H NMRspectrum was consistent with L-glufosinate and showed no residualorganic solvent. Ion chromatography analysis of a different Form Bsample showed only minor ammonium content (0.17 wt %) suggesting thatForm B is not the ammonium salt but rather a crystalline form of theL-glufosinate zwitterion. Thermal analysis of the sample (FIG. 4 ) wasconsistent with a nonsolvated/anhydrous crystalline form. No significantthermal events were observed prior to a large endotherm at 123° C.(onset). A significant change in the slope of the TGA was also observednear this temperature suggesting this is a likely melt/decompositionevent. No significant changes were observed in the XRPD pattern of thesample upon storage over desiccant for 47 days.

3. Form C

Form C with minor Form A was prepared via stress of L-glufosinateammonium with MeOH vapor. The XRPD pattern for Form C was indexed,however several peaks were observed that are consistent with Form A(FIG. 5 ). The ¹H NMR spectrum was consistent with L-glufosinate howeverion chromatography indicated that the ammonium content wassub-stoichiometric (6.3 wt % compared with 9.1 wt % for a theoreticalmono salt and 7.0 wt % for the as-received material).

The sample of Form C with minor Form A was stored under desiccant for 36days and XRPD analysis of the sample showed conversion to Form B withminor Form A and a few minor additional peaks. IC analysis also showed asignificant loss of ammonium content over that time (3.2 wt % vs 6.3 wt% initially). The results suggest that Form C is metastable and prone toform conversion/dissociation of the ammonium salt on long term storageunder desiccant.

Form C with minor Form A was successfully re-prepared via vapor stresswith MeOH. ¹H NMR analysis of the new sample was consistent with thechemical structure of L-glufosinate. Thermal analysis showed twooverlapping broad endotherms at 100° C. and 131° C. (FIG. 6 ). A weightloss of ˜10 wt % was observed with the endotherms followed by gradualweight loss upon continued heating.

4. Form D

Form D was prepared from several room temperature or elevatedtemperature slurries in the polymorph screen, typically as a mixturewith Form A. A mixture of Form A and Form D was found to be consistentwith the chemical structure of L-glufosinate by ¹H NMR analysis. Nosignificant changes were observed in the XRPD pattern of a sample ofForm D+ minor Form A upon storage over desiccant.

Form D was isolated from a three day slurry at 60° C. in 50/50 v/vTFE/acetone. The XRPD pattern of Form D (FIG. 7 ) indicated that thesample is composed primarily or exclusively of a single crystallinephase. Ion chromatography analysis indicated 2.3 wt % ammonium contentwhich is significantly less than would be expected for a theoreticalmono ammonium salt (9.1 wt %). Based on the substoichiometric amount ofammonium present, Form D is likely a crystalline form of theL-glufosinate zwitterion. Thermal analysis of the sample (FIG. 8 )showed consistent gradual weight loss and a change in slope around 151°C. suggestive of the onset of decomposition. A very broad endotherm wasobserved with an onset of ˜140° C. suggestive of a melt/decompositionevent.

5. Form E

Form E was observed during initial screening, as an as-received sample,and as a sample crystallized from aqueous acetone with HCl. The ¹H NMRspectrum of Form E was consistent with L-glufosinate with peak shiftingsuggestion potential ionization differences. IC analysis showed only atrace amount of ammonium along with a stoichiometric amount of chloride.The results suggest that Form E is not a form of L-glufosinate ammoniumbut a form of L-glufosinate HCl.

6. Amorphous Material

X-ray amorphous material was collected from slurries in solvents such asN-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), and2,2,2-trifluoroethanol (TFE), which were maintained at temperaturesranging from 50° C. to 60° C. for extended periods (e.g., 12 days). ¹HNMR analysis of amorphous L-glufosinate ammonium was consistent with thestructure and showed the presence of minor unknown peaks. Thermalanalysis of the material revealed an apparent glass transition, Tg, at˜55° C.

It is understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and the terminology is notintended to be limiting. The scope of the invention will be limited onlyby the appended claims. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the invention, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.Certain ranges are presented herein with numerical values being precededby the term “about” or the term “around”. The term “about” and “around”are used herein to provide literal support for the exact number that itprecedes, as well as a number that is near to or approximately thenumber that the term precedes. In determining whether a number is nearto or approximately a specifically recited number, the near orapproximating unrecited number may be a number, which, in the context inwhich it is presented, provides the substantial equivalent of thespecifically recited number. If “X” were the value modified by “about”or “around,” “about X” or “around X” would generally indicate a valuefrom 0.95X to 1.05X including, for example, from 0.98X to 1.02X or from0.99X to 1.01X. Any reference to “about X” or “around X” specificallyindicates at least the values X, 0.95X, 0.96X, 0.97X, 0.98X, 0.99X,1.01X, 1.02X, 1.03X, 1.04X, and 1.05X. Thus, “about X” and “around X”are intended to teach and provide written description support for aclaim limitation of, e.g., “0.98X.”

All publications, patents, and patent applications cited in thisspecification are incorporated herein by reference to the same extent asif each individual publication, patent, or patent application werespecifically and individually indicated to be incorporated by reference.Furthermore, each cited publication, patent, or patent application isincorporated herein by reference to disclose and describe the subjectmatter in connection with which the publications are cited. The citationof any publication is for its disclosure prior to the filing date andshould not be construed as an admission that the invention describedherein is not entitled to antedate such publication by virtue of priorinvention. Further, the dates of publication provided might be differentfrom the actual publication dates, which may need to be independentlyconfirmed.

It is noted that the claims may be drafted to exclude any optionalelement. As such, this statement is intended to serve as antecedentbasis for use of such exclusive terminology as “solely,” “only,” and thelike in connection with the recitation of claim elements, or use of a“negative” limitation. As will be apparent to those of skill in the artupon reading this disclosure, each of the individual embodimentsdescribed and illustrated herein has discrete components and featureswhich may be readily separated from or combined with the features of anyof the other several embodiments without departing from the scope orspirit of the invention. Any recited method may be carried out in theorder of events recited or in any other order that is logicallypossible. Although any methods and materials similar or equivalent tothose described herein may also be used in the practice or testing ofthe invention, representative illustrative methods and materials are nowdescribed.

1. An L-Glufosinate crystalline form, the crystalline form,characterized by an X-ray powder diffraction (XRPD) pattern comprisingat least three peaks selected from 9.1, 11.6, 13.1, 14.1, 14.4, 16.2,17.7, 18.2, 18.9, 19.3, 19.7, 21.2, 21.8, 22.4, 23.2, 23.5, 25.3, 25.8,26.2, 27.2, 28.6, 29.1, 30.0, 30.6, 31.1, 31.6, 32.7, 33.5, 34.4, 34.7,35.4, 35.9, 36.4, and 37.4° 2θ, ±0.2° 2θ, as determined on adiffractometer using Cu-Kα radiation.
 2. The L-Glufosinate crystallineform according to claim 1, wherein the XRPD pattern comprises at leastsix peaks selected from 9.1, 17.7, 18.2, 18.9, 22.4, 23.2, 23.5, 26.2,33.5, and 36.4° 2θ, ±0.2° 2θ.
 3. The L-Glufosinate crystalline formaccording to claim 1, wherein the XRPD pattern comprises peaks at 9.1,17.7, 18.2, 18.9, 22.4, 23.2, 23.5, 26.2, 33.5, and 36.4° 2θ, ±0.2° 2θ.4. The L-Glufosinate crystalline form according to claim 1, wherein theform has the XRPD pattern of FIG. 7 .